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ADM 1/9387: CAPITAL SHIPS-PROTECTION (1935)
Updated 31-Mar-2009

This document is a modern transcription of Admiralty record ADM 1/9387. It highlights considerations and factors concerning proposed battleship/battle cruiser designs as well as the vulnerabilities of existing ships. It was transcribed by David Chessum on behalf of the the Royal Navy Flag Officers 1904-1945 website. The original file is held at the The National Archives at Kew, London. This Crown Copyrighted material is reproduced here by kind permission of The National Archives.

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Minute Sheet No 1.

Register No. T.D. 151/35

 

Remarks on the protection of Capital Ships are submitted herewith. DNC’s department has been consulted, but the question has not been referred to DNC officially.

F.A. Buckley […]
D.T.S.D. for D. of T.D.
2.8.35 2.8.35

The question of what protection and speed is required in a new battle cruiser is discussed in this paper.

2. Following the principle worked to in the case of the HOOD, a battle cruiser’s protection should be the same as that of a battleship. The protection must, therefore, depend on what the decisive fighting range is to be, assuming an equal calibre of gun on either side. The Battle Instructions state 12,000 – 16,000 yards.

3. The argument for increasing this and thereby saving weight is that, with modern control arrangements and air spotting, really effective fire can be produced at greater ranges, say 18,000 – 20,000 yards.

The argument against any increase is that, when and if the means of air spotting are destroyed with possibly the finer fire control arrangements, effective and decisive results cannot be obtained in the confusion and smoke of battle outside the ranges laid down in the Battle Instructions, and tat ships should be capable of coming into the shorter ranges.

4. Added to these arguments is the problem of the use of Inclination by the fast battle cruiser to provide additional security, given equal deck protection.

5. As regards speed, while it may prove necessary to accept a lower speed than 30 knots in order to provide for armour protection and offensive armament, I am much averse to this and am not convinced that we can deliberately sacrifice 2 or 3 knots without serious loss of tactical power.

6. The practice hitherto has been to provide lighter deck armour over machinery spaces than over magazines. Whether this policy should be amended or not requires examining. It is largely a question of weight.

7. Before formulating the staff requirements for a battle cruiser, apart from the present unknown factor of what the gun calibre is to be, the following major points require decision:-

(a) What is to be the decisive fighting range, assuming that a battle cruiser must be as capable as a battleship of fighting at this range?
(b) Is inclination to be taken into account, when working out thickness of armour?
(c) What is the speed to be aimed at?

8. Other points are:-

(d) Is deck armour to be uniform over magazines and machinery spaces?
(e) What weight and height of bomb is to be allowed for?
(f) What weight of underwater charge is to be taken into account?

9. The final point on which all else eventually hangs is -

(g) What is the minimum acceptable armament?

Too high a limit will cause loss of protection and/or speed; too low a limit will give a ship with weak offensive power.

10. I suggest that these points be discussed as soon as possible so that the staff requirements and preliminary designs by D.N.C. may be worked out.

[…]

7th August, 1935.

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Minute Sheet No 2.

Register No. T.D. 151/35

 

Would you have time to deal with this question before you proceed on leave, or in any case to give your general view as to what is to be the requirement which we can then communicate to Controller. I feel reluctant to forego the advantage of closing to a range of 12,000 yards as the power to do this may form a valuable tactical surprise.

[…]

7th August, 1935

This must be discussed at a Sea Lords meting in mid Sept’. Papers to be circulated.

[…]

9.8.35

An appendix has been added to this memorandum giving more information to assist in this consideration of the points raised in my previous minute of 7/8/35.

[…]

16.8.35

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Minute Sheet No 3.

Register No. T.D. 151/35

 

This question was discussed on 20th September, 1935, at a meeting of the Sea Lords who also had before them a Memorandum prepared by the Tactical Division which examined the considerations governing the choice of gun and protection (T.D. Memorandum 136 of 16 th September, 1935).

The conclusions of the Sea Lords were as follows:-

(a) That the first 2 Capital Ships should be of 35,000 tons, 9 15-inch guns, speed not less than 29 knots, with protection as in design 14.D.* based on German new construction, and that this design should be duly investigated in detail. It was noted that the value of protection assumed in the designs under review may have to be modified as a result of the anticipated performance of projected gun designs.

* (For particulars of this design see Appendix to T.D. Memorandum 136)

(b) That we were willing to reduce the size of subsequent ships if we could get international agreement.
(c) The Controller was asked to instruct the D.N.C. to look into the question of the “margin” the general feeling that we should design up to the limit and if it turned out there was any weight to spare it should be utilised in increasing the protection of the Secondary Armament.
(d) The Controller was asked to look into the question of providing shelter (say 1½-inch splinter screen) for the large number of ratings manning the Secondary Armament.
(e) The replies to two questions put forward by D.C.N.S. in a separate paper dated 19th September, 1935, were as follows:-

(a) “Do we desire to press for a subsequent qualitative limit of 1-inch guns and a lower tonnage?”
Reply. Yes mainly for economical and political reasons.

(b) “What tonnage is acceptable for the qualitative limit of a 14-inch gun Capital Ship of the future?”
Reply. This could not be stated until we knew the size of gun proposed by the United States. The first action should be to settle the size of the gun and then try to get some agreement as to tonnage. It was, therefore, agreed that even if the United States adhere to the 16-inch gun our policy would be to adhere to the 15-inch in our first new ships. The possible necessity of having to build two battleship types had always been visualised and it might be that the first 5 should be built to meet the German design and the later 10 to meet the Japanese when it was seen what they intended to build.

[…]

24th September, 1935 .

D.N.C.

Please go ahead with […]

[…[

24.9.35

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PROTECTION OF CAPITAL SHIPS

The Protection of capital ships is here examined to illustrate the sacrifice to be accepted if high speed is to be incorporated in the design.

2. It is generally accepted that we cannot afford the luxury of a Battle Cruiser which is unable to stand in the line. She must, in fact, be a fast Battleship. From this it follows that the Battle Cruiser, though perhaps of less gun power and less able to stand up to close range fire, must be as well protected as the battleship for closing to a reasonably effective range; until ascendency has been gained she may then have to use her speed to remain at an effective, but favourable range for herself.

Decisive Range

3. The Battle instructions, Clause 9 (g), state that a decisive range of between 12,000 and 16,000 yards will be aimed at and the reasons for this choice would appear to be as follows:-

4. Decisive actions only occur when both sides either wish to fight or when one or other cannot avoid action, in which case “fighting power” and not speed is the ultimate requirement. The decision may well depend finally on the morale and striking power of our fleet at short range; a range should therefore be chose which gives morale the greatest opportunity, where the rate of hitting is high and the factor of luck low, where the enemy (through short time of flight and large danger space) is least able to avoid punishment, but where our own ships are not liable to destruction by magazine explosions – by the lucky hit.

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5. When the battle reaches this stage, air spotting and the primary control positions, with many of the refinements of fire control, may well be out of action, having, it is to be hoped, contributed to gaining an ascendency during the earlier stages. Although air spotting can give effective hitting and perhaps even a decision, for the final destruction of the enemy we must be prepared to close to a range where direct spotting is possible in the confusion and smoke of battle, and where hits can be assured.

6. For these reasons, action ranges of 12,000 to 16,000 yards must be provided for in spite of the advance in air spotting and fire control, and the design of the modern and reconstructed ships permit them to fight at these approximate ranges against 14-inch fire.

Modern Protection.

7. The attached tables and graphs show that in the suggested 197 Battle Cruiser (35,000 tons) the armour belt is pierced by the 14” high velocity gun at a 2,500 yards higher range than in the 1937 Battleship (Design “Q” – 32,800 tons – 3 Quadruple 14” – 23 kts.), but that these ships are similar with regard to plunging fire and protection against bombs.

The 1937 Battleship, on the other hand, is inferior to NELSON in that her belt is pierced at a range 3,000 yards higher than in NELSON, who has also considerable advantage in deck protection. This is understood to be due to the economical distribution of the armour, inherent in the type of design and to the belt being inclined and inboard, which gives a more favourable striking angle for the armour and slightly reduces the area of the protected deck. The inclination fo the belt has, however, the possible disadvantage

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of deflecting shell to the ship’s bottom and may therefore be unacceptable in future design.

Closing the range.

8. As compared to NELSON, both the 1937 ships would be at a disadvantage against plunging fire of 14” guns between 29,000 and 26,000 yards. Hits at this range, though possibly rare owing to the long time of flight and small danger space, are most effective.

9. It may perhaps be said that the speed of the Battle Cruiser will permit her to close through this danger zone fairly quickly, and she would then be on even terms with NELSON (14” fire) as regards protection until she reaches 19,000 yards, when at 90º inclination her machinery compartments will be open to damage through the belt. If closing further without grave danger of vital damage she would have to rely on her speed to remain at a favourable inclination.

10. By comparison with the 1937 Battleship, the Battle Cruise would be equally protected until closing to 19,000 yards, when she would have to close through a 2,500 yards zone before the Battleship’s belt could be pierced at 90º inclination. Again, during this period, she would have to rely on her speed to remain at a favourable inclination.

Deck Protection.

11. The decks of both the 1937 ships would appear to be adequate against bombing, but the advantage in NELSON against plunging fire is important. With air spotting, hits between 29,000 and 26,000 yards are practicable, particularly when direct laying and training are possible.

To provide the Battle Cruiser with reasonable

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certainty of being able to reach an effective range, it would seem essential that no sacrifice be made in deck protection. This principle has been accepted in the 1937 Battle Cruiser by comparison with the 1937 Battleship, but it is desirable that both these ships should more nearly approach the NELSON standard against plunging fire.

The balance between armament, protection and speed.

12. It is not here proposed to examine in detail the value of speed by comparison with fighting power, but three points would appear to be outstanding:-

(i) In the event of a decisive action developing (para. 4. above) ‘fighting power’ will ultimately be the main requirement of capital ships.
(ii) Fast capital ships might be required to deal with similar foreign ships, not so much in a major fleet action, but rather when detached on harassing operations.
(iii) What is suitable against one country may not be the best construction when considering another possible enemy, e.g., Battle Cruisers would be of less importance against Japan than against European powers who are building this type of ship; in fact, against Japan, the sacrifice of fighting power in the battle fleet resulting from building Battle Cruisers may be most undesirable at present.

13. Assuming that it be decided that strategically and on the grounds of morale and prestige, a proportion of

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fast capital ships is an immediate requirement, and that it is probably that corresponding foreign ships will attain 30 knots, it is for consideration what is the minimum speed we can accept, having regard to the gain in fighting power resulting from a lower speed.

14. War experience suggests that, where speeds are comparable, the strategic and tactical considerations have a greater influence on bringing a superior force to bear at the decisive time and place than has the ability to develop equal or even, within limits, a greater speed.

15. With this in mind, and considering the fleet as a whole, with its fighting power and reconnaissance forces, it is suggested that we should deliberately accept a lower speed, say 27 or 28 knots, if investigation shows the resulting gain in fighting power to be worth while.

16. This difference in maximum speed will have but little effect in the plane of strategy; such factors as the position of bases, intelligence, reconnaissance, plan and disposition of forces, will generally outweigh the practical effect of a margin of 3 knots on one side.

17. Tactically it must be our utmost endeavour to bring superior reconnaissance to bear and the development of air reconnaissance to some extent reduces the value of superior speed, in that greater opportunities are afforded for gaining that position which should ensure interception even if our speed is slightly inferior. Interception having been effected, Fighting Power is the main requirement.

CONCLUSION

18. The figure, 3 knots less speed, cannot at present

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be supported by detailed argument and data, and it is suggested that D. of N. Might examine a number of typical situations to test the validity of the proposal.

19. It is further proposed that D.N.C. should examine the gain in fighting power (i.e., armament or deck protection of armour belt), which could be expected if a reduction of 3 knots in the Battle Cruiser were accepted.

20. Underwater protection is a separate problem and is not here examined the main development being the greatly increased watertight subdivision, which also limits damage by gunfire and has a bearing on the belt and deck protection.

21. Previous investigations into the protection of capital ships are included in “The Characteristics of the Battleship – Staff paper, June 1933” – which this paper summarises and brings up to date. These past examinations have illustrated that if the principle of “corresponding protection” be departed from, and ill balanced ship is likely to result – i.e., a 14-inch gun ship, protected against 16-inch fire, is unduly large for her gun power.

22. If it be decided to increase the protection of the Battle Cruiser with sacrifice of speed, the decision whether it should be applied to the deck or belt will be influenced by the distribution of armour and the virtual target presented at various ranges, a matter for detailed investigation; but it would appear from para. 11 above the improvement of the deck protection is the more important.

It must be recalled that the use of inclination may assist side armour, but no such measure can assist the deck to resist bombs.

August, 1935.

(T.D. Memo. No. 132.)

Appendix – attached.

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(Appendix to T.D. Memo. No. 132.)

PROTECTION OF CAPITAL SHIPS.

The following information is added to the Memorandum to facilitate a decision on the points raised by A.C.N.S. This Appendix summarises recent discussions on the Staff Paper “The Characteristics of the 1937 Battleship” compiled in 1933.

2. Decisive Range and Speed.

These points are remarked on by A.C.N.S., and in the Memorandum, and D. of N. has been requested to examine the possible implications on the proposal to reduce the speed.

3. Protection against Gunfire.

A fast ship fighting against slower ships can use her speed in some measure to dictate the range and to place her side armour at a favourable inclination.

On the other hand, no manoeuvre of this sort can assist her deck armour to resist plunging fire – except in so far as turrets and other obstructions reduce the deck target at fine inclinations.

4. Protection against Bombs.

Even if the “B” Bomb should replace other bombs for sea service powerful deck armour is still required for defence in harbour.

High bombing, though much less likely to hit than Dive Bombing, has greater penetrating effect.

Decks which protect against High Bombing above 5000 feet will keep out the same bomb used with Dive Bombing.

As with plunging fire, nothing we can do in the way of manoeuvre can assist the deck to resist a hit by a bomb.

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Appendix (cont’d)

The percentage of hits with unseen High Bombing may be as high as 15%, but if seen the long range A.A. fire goes far to meet the menace.

The 2000 lb. Bomb is possible, but it is far more likely that attackers would prefer to use numbers of smaller bombs than a few of 2000 lbs. It is not likely that Dive Bombing will be practicable with more than 1000 lb. bombs.

5. Magazines and Engine Rooms v. Bombs.

It has been held that magazines must be protected against the largest bomb reasonably likely to be used, but for the machinery spaces les protection must be accepted, reliance being placed upon the sub-division of the ship.

In the recent tentative Battleship designs, the magazines were protected against the 1000 lb. Bomb up to 12000 ft., and the machinery spaces against the 500 lb. Bomb, which it is though is the probable sea service bomb.

6. The question is – are we allowing for sufficient weight of Bomb, particularly for magazines?

The following table show the protection value of various decks.

10000 to 12000 ft. is regarded as a reasonable Bombing height.

Heights above which the deck will be perforated.


Deck.

2000 lb.
A.P. Bomb.
ft.

1000 lb.
A.P. Bomb .
ft.

500 lb.
S.A.P. Bomb .
ft.

4”

3000

7000

12000

5”

5000

10500

Immune

6”

7000

10500

- do -

7”

9000

Immune

- do -

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Appendix (Contd.)

7. Under Water Attack.

It does not appear likely, though it is possible, that a warhead of more than 750 lbs. will be developed for use from destroyers, submarines and aircraft.

To use weight for bulge and other protection against a large warhead in contact would seem waste of effort when the most probable form of attack will be the contact-non-contact pistol and “B” Bomb under the bottom – against which W.T. sub-division of the ship is the only defence. We must at present accept the possibility of a main compartment being flooded in this way.

8. W.T. Sub-division.

The W.T. Sub-division forced on us by the “non-contact” threat, and facilitated by modern machinery design, has an important bearing on the isolation of damage by gunfire or bombs except for the magazines.

It is for consideration how far this sub-division permits us to accept less protection for important compartments other than magazines, for the sake of offensive power.

T.D.

16.8.35

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CAPITAL SHIPS

CALIBRE OF GUNS
AND PROTECTION

Tactical Division
     Naval Staff.
       (T.D. Memo. No. 136)
         September, 1935.

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CAPITAL SHIPS.

CALIBRE OF GUNS.

To decide the calibre of the gun it is first necessary to investigate the effect of various mountings on the other two main characteristics of the ship – PROTECTION and SPEED – if a proper balance between offence and defence is to be reached. “Defence” is a somewhat misleading term as applied to armour protection against gunfire; for, in circumstances where it enables our guns to reach the vitals of the enemy before his can reach our vitals, armour is by no means a purely passive defence – it secures our offensive.

2. It is generally accepted that a capital Ship, whether Battleship or Battle Cruiser, must be sufficiently powerful to contribute effectively in the battle line, and to withstand aircraft and torpedo attack so far as possible. It is only necessary at this stage to examine the protection in general terms, the detailed distribution being decided upon later.

3. The outline designs have been analysed in the attached tabular statement after consultation with D.N.C., and the examination is here made purely fro the fighting point of view without other treaty considerations than a displacement limit of 35000 tons.

4. It is assumed that the maximum displacement must be 35000 tons, and the problem is examined below under the following main headings

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Comparison of guns.

The 30 knot ship.

The 27 knot ship.

The 23 knot ship.

NELSON Design.

The General Problem.

5. To clear the issue the following general conclusions resulting from the investigation are outlined below:-

(i) For a given displacement and speed there appears to be a correct balance of armament and protection, and, in the faster ships it seems that this can generally be attained by one of two calibres of gun separated by not more than 1 inch. The extra protection possible with the smaller gun compensates for the superior hitting power of the larger gun.
(ii) A slower ship of the same displacement can be so well protected that no additional protection can usefully be added as a result of mounting the smaller gun. The problem is then that of estimating the value of more numerous and smaller guns, as compared with fewer heavier guns, in their shattering effect before decisive range is reached.
(iii) Unless the ship with the light gun is adequately protected against the heavier gun, the advantage she gains by greater numbers is outweighed by the vulnerability of her vitals.
(iv) It appears that neither 9-16” nor 12-14” can be mounted in a 30 knot ship with sufficient protection.
(v) A well balanced 30 knot 15” ship can be designed which is a match for the ships mentioned in (iv) and which is better able to stand in the line.
(vi) At 27 knots there is no great difference between the 16” and 15” ships, and they are both superior to the 14”
(vii) For a 23 knot ship the 16” gun seems undoubtedly the best unless 12-15” or 12-14” can be mounted. The more numerous guns might tell at medium or long ranges, but the 16” would be greatly superior at decisive ranges.
The inclusion of four turrets congests the design.
(viii) If a new limit of displacement be assumed, it is not justifiable to draw conclusions from the following analysis.

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6. The Tabular Statement

The graph shows the approximate performance of the belt against 16”, 15” and 14” fire. The lower the lines on the graph the better is the belt protection.

The approximate ranges at which the decks are penetrated by 16” plunging fire are also shown on the graph. In this case, the higher the spots on the graph the better the deck protection.

The value of the decks against bombs is estimated in the bottom table.

7. Decisive Range.

On T.D. 151/35 (Protection of Capital Ships), it was suggested that in spite of the advance of Air Spotting and Fire Control, Capital Ships must still be designed to fight at between 12000 and 16000 yds, as it may well be necessary to close to a range where direct spotting is possible in the smoke and confusion of battle, with, perhaps, air spotting and many of the refinements of fire control out of action.

In these remarks, therefore, the term “ Decisive Range” is used to indicate ranges from 12000 to 15000 yds., which are those given in the Battle Instructions; and the term “Battleship Protection” implies that the vitals are protected at these approximate ranges.

8. The value of speed as protection during action.

A superiority of speed if sufficient, is of undoubted tactical value in certain circumstances to enable an action to be forced or to be avoided.

The statement, however, that speed can afford protection in action is only true to a limited extent and may

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be misleading. Speed has a value for protection in Capital Ships in so far as it enables the fighting range to be dictated but this does not apply when the margin of speed is mall, or in low visibility.

It is also sometimes said that the fast ship can use her speed to keep her armour at favourable inclination, and thus increase its protective value.

It is very open to question whether, in the uncertainties and varying conditions of contact and battle, the fast ship could in fact dictate the range or the inclination of her armour except perhaps when fighting a ship very considerably slower than herself. The value of speed purely as protection in battle cannot therefore be relied upon.

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COMPARISON OF GUNS.

9. The considered below are:-

NELSON’s 16”
American 14” H.V.
British new 15” (estimated).

These guns are considered typical of modern attack and, if the ship is to stand in the line, smaller guns need not be considered (see note to attached tables).

The Italian 15” is reported to have an abnormally high M.V., but it is understood to be unlikely that its striking energy will exceed that of the new British 15”.

10. The factors to be considered in the comparison of guns are shown in the following table:-

 

14” guns.

15” guns.

16” guns.

Weight of shell

1590 lbs.

1938 lbs.

2375 lbs.

Weight of burster

49 lbs.

48.5 lbs.

59.5 lbs.

20,000 yds – Time of flight.

31 secs.

30.5 secs.

30 secs.

20,000 yds - Danger space of 30 ft. target

35 yds.

35 yds.

35 yds.

Loading interval.

Details not available; with similar turret designs there will be little or no difference in rate of fire.

Maximum range.

Sufficient in all cases.

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11. It is evident from the above that “Hitting Power”, as affected by striking energy and the explosive power of the shell, and “Chance of Hitting”, as affected by the number of guns per salvo, are the important factors. It is therefore the basis that the comparison is made below; rate of fire time of flight, etc., are not taken into account.

Hitting Power.

12. The means by which gunfire can reduce the fighting efficiency of an opponent are:-

13. For penetrating the vitals it is evident that, against equal protection, the larger gun has the advantage, whether through the belt or the deck.

14. The shattering effect may be of particular importance when fighting at ranges at which neither ship’s armour can be pierced; in these circumstances, the smaller, more numerous guns should hit more often, but this must be weighed against the extra explosive power of her opponents’ larger shell and the advantage she has in penetration.

Chance of Hitting.

15. It is here assumed that an increase in the number of guns per salvo results in a proportional increase in the hits to be expected. The exact truth of this assumption in practice is perhaps open to doubt, but it is a fact that the chance of hitting is improved by the extra rounds “packing the salvo” to some extent, and by the fact

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that the increased spread ay enable the target to be found and held more readily.

16. For the number of guns here considered (4 to 6 guns per salvo) this assumption may give an unduly favourable view of the more numerous guns.

The heavy gun is widely favoured in our Service, but it must be recognised that both size and number of guns are important considerations. The assumption made in para. 15 above has therefore been accepted in order to give full weight to the argument for the more numerous armament.

17. In the comparison of fighting power, as represented by gun power, protection and speed, on the basis of the attached tabular statement, it is realised that conclusions must be drawn with caution. The figures used cannot be taken as exact, particularly with regard to Deck Protection.

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The 30 Knot Ship.

18. The following assumptions are made:-

Designs 14C & 16A

19. These ships are vulnerable to vital damage by 16” & 15” through their belts considerably outside decisive range; they are not well protected against 14”, and their machinery compartments are unduly open to plunging fire and bombs, particularly 16A within her 3” deck.

20. It might appear that 14C would have some advantage in the shattering effect of her 12 guns upon unprotected parts. According to the assumption made in paragraph 15 she might expect to obtain 4 hits to every 3 scored against her by the 16” ship, but this advantage must be balanced against the explosive effect of individual 16” hits, which is 1½ times that of a 14”, and against the considerable extra penetrative power of the 16” shell.

21. Both these ships are considered to be over gunned for 30 knot ships of 35,000 tons; it will be seen from the comparisons made below that they are too lightly protected to stand up against other 30 knot Battle Cruisers shown in the table, and that they could not contribute effectively in the Battle line without grave risk of damage

Designs 14 E and 15A

22. These 30 knot ships have similar protection except that the machinery deck of 15A is weaker than that of 14E by about 3,000 yards against 16” plunging fire.

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Neither ship could stand in the battle line at decisive range without grave risk, but they could contribute usefully at about 19,000 yards against 16” and 15” fire.

Against each other, 15A appears the better shp; she has the greater hitting power her protection against 14” is better than that of 14E against 16”, and her 9-15” would compare favourably in all respects with her opponents 10-14”.

In the comparisons made below it will be seen that 15A in spite of her somewhat weaker machinery deck is also better than 14E for fighting against other ships or when standing in the line, because of the superior hitting power of her 15: guns.

Design 14D.

23. Although her protection is good, this ship is considered to be under gunned, whether with 8-14” or 6-16”. Six 16” guns would not be satisfactory from the fire control point of view, and reference to the table shows that the 14” has inadequate hitting power against eh protection which can be provided in a 30 knot ship of greater gun power than 8-14” (i.e. 15A or 14E).

This ship is not further considered in this analysis.

Comparison between 15A and 14C.

24. The 15” guns should reach the vitals of 14C through her belt at about 19,000 yards whilst her own belt should hold against 14C’s 14” fire down to about 15,000 yards; 15A’s decks are considerably superior to those of 14C.

These advantages, together with the extra explosive power in the 15” shell, are considered to outweigh the superior volume of fire from the 12-14” guns of 14C, which it is assumed would give 4 hits to every 3 obtained by the 9-15”.

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Comparison between 15A and 16A

25. The 15” guns should reach the vitals of 16A through the belt slightly before her own are vulnerable to 16” fire, and the 15” plunging fire should pierce 16A’s machinery deck at about 21,000 yards whilst her own decks hold out 16” fire up to 25,000 yards.

Taking into consideration the extra explosive power of the 16 inch shell, there seems little to choose between these ships when fighting against each other. But if both ships had to stand in the battle line against 16” or 15” fire, 15A’s belt would have an advantage of about 2,500 yards, and her decks 3,000 yards. 15A is also better against air attack.

On the whole therefore, owing to 15A’s comparatively light protection, particularly the machinery deck, 15A is considered the better balanced ship.

Note. 14E, with her 10-14” and similar protection to 15A, does not compare so favourably with 16A, whose 16” shell can pierce 14E’s belt at 18500 i.e.1,000 yards before her own belt is vulnerable to 14” fire.

26. Protection against bombs.

This problem is not here examined in detail, but it has a bearing on the decision regarding the calibre of gun to be mounted, because it affects the weight available for the armament.

The Decks required against plunging fire are comparable with those required against bombs; it would appear that the Deck protection should be of the order of that in 14D or E and that, on both grounds the plunging fire or bombs 14C and 16A have not sufficient Deck protection.

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27. The 30 knot ship – Conclusions.

(i) 14” guns.

All ships, except 14C and 16A can be well protected against 14” fire.

Except when the armament is greatly reduced as in 14D, the 15” and 16” guns can reach the vitals of a 14” ship before her 14” guns can penetrate the protection of the more heavily gunned vessels.

It appears, therefore, that the 14” gun should be ruled out unless required by treaty.

(ii) 16” guns.

16” guns cannot be mounted in a 30 knot ship with adequate protection (16A); such a ship could not be expected to stand in the Battle line without grave danger of vital damage.

(iii) 15” guns.

The 15” gun can be mounted in a comparatively well protected ship (15A), who has good Decks and whose Belt would permit her to close against 16” fire to about 19,000 yards. The 30 knot 15” ship would incur grave risk at Decisive Ranges, but she is able to contribute effectively in the battle line at useful ranges and would, individually, be a match for any 30 knot 16” or 14” ship of 35,000 tons.

The conclusion is reached that the 15” gun is the best armament for a 30 knot ship of 35,000 tons displacement.

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THE 27 KNOT SHIP.

28. The effect on armament and protection of a 3 knot reduction in speed is shown in designs 14F, 15B, 16B and 16C.

The strategical and tactical effect of this reduction is under discussion in T.B.151/35.

The arguments against such a reduction are self-evident, but the advocates of the slower ship urge that the resulting gain in fighting power may well outweigh the disadvantage of the slower speed. It is suggested that decisive battles do not occur as a result of slightly superior or equal speed of capital ships; an unwilling enemy with freedom of movement can generally avoid action unless strategic factors, or our “position”, gained by reconnaissance and the use of all arms of the fleet, force him to fight.

If our opponent should build 27 knot ships whilst we build 30 knot ships, we should be at a disadvantage in that, although our speed might enable us to overtake the enemy we would be of less fighting power.

29. The 27 knot designs examined are:-

(I) Design 14 F.

12-14”, protection similar to 14E. with slightly inferior decks 0 speed 27 knots.

(II) Design 15 B.

9-15”, Battleship protection as in 14D, speed 27 knots.

(III) Design 16 B.

8-16”, Battleship protection as in 14C, speed 27 knots. The arrangement of 2 Triple and one pair gun turret is not satisfactory and this ship is not here examined in detail.

(IV) Design 16 C.

9-16”, protection as in 14 E, speed 27 knots. This design is an estimation only, derived from the weights given for 16 B and 16 A.

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30. Comparison is here made purely on the basis of fighting power in order to assess the gain resulting from a sacrifice of 3 knots; and this margin was chosen as that which, whilst enabling an addition of fighting power, si insufficient to permit the faster ship to dictate the fighting range with any certainty – if strategical, tactical or weather conditions should force her to fight.

31. It has been suggested above that 16 A, and 15 A, are the best 30 knot ships, and the 27 knot ships (14 F, 15 B, 16 B and 16 C) are therefore compared with these.

Comparison of 14 F (27 knots) with 16 A or 15 A (30 knots).

32. It is difficult to assess the comparative fighting value of 14 F with 16 A or 15 A.

As compared to 16 A, 14 F, has a valuable superiority in deck protection.

She should obtain 4 14” hits at useful ranges to every 3 16” hits by her opponent. 16 A would gain an advantage at 18,500 yards, by being able to pierce 14 F’s belt 1,000 yards before 14” guns can reach 16 A’s vitals. 14 F would b better able to stand in the line than 16 A.

Against 15 A, similar remarks apply, except that 14 F has not in this case so great an advantage in deck protection, but she is able to close to a more effective range for bringing her high volume of fire to bear.

It would appear that 14 F is as powerful as 16 A or 15 A, and she has an asset in her good decks and Torpedo bulkhead.

Comparison between 15 B (27 knots) and 16 A or 15 A (30 knots).

33. Against 16 A, 15 B has a 2,500 yard advantage in belt protection and greatly superior decks.

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Against 15 A she is about equal when between ranges of 27,000 and 17,500, when neither ship’s vitals are vulnerable. 15 B, having better decks and belts is more able to withstand air attack and to close to decisive range.

Comparison between 16 C (27 knots) and 16 A r 15 A (30 knots).

34. The same method of comparison shows that 16 C is of definitely superior fighting power to 16 A or 15 A.

Comparison between 15 B (27 knots) and 16 C (27 knots).

35. When fighting against each other the protection of 15 B against 16” fire is about the same as that of 16 C against 15”; and there is little to choose between the two ships other than the superior explosive effect of the 16 inch against unprotected parts, and the somewhat better protection of 15 B against bombs.

If both ships were in the line against Battleships, again there is little to choose because, although the armament of 16 C has a greater shattering effect, the protection of 15 B enables her to close to 17,000 yards for decisive results (2,000 yards closer than 16 C could close without serious risk). 16 C would also be slightly more vulnerable to plunging fire, and her torpedo bulkhead is lighter than that of 15 B.

36. These considerations lead to the conclusion that a well balanced 27 knot ship can be built, either with 9-16”, 9-15: or 12-14”. For fighting against battle cruisers 16C (9-16”) is probably the best, but 15 B may be considered the better general service ship, because she can contribute in the battle line better than the 16” or 14” ships, and she will be a good match for any battle cruiser.

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THE 23 KNOT SHIP.

37. From the figures given for NELSON, 14 Q and 16 A, it appears that a 9-16” ship could be designed with one turret aft, and that she might have full Battleship protection as in 15 B.

38. To mount 15” guns in this ship would be of little use unless a considerable increase in numbers were possible, and it appears unlikely that 12-15’ could be included. The protection is already adequate, so the weight saved by mounting 9-15” would only be employed in a reduction of displacement.

39. A 12-14” gun ship would gain in the number of hits over a wide and useful zone down to about 17,000 yards, when 16” guns could pierce her vitals. No definite conclusion can be drawn in this respect, but it appears that the extra hitting power of the 16 inch, combined with its penetrative power at decisive range, would tip the balance in favour of the larger gun.

NELSON DESIGN.

40. Although it is not desired to re-open detailed discussion on this design, it is necessary to examine the effect on the armament if adopted, if only to see what our opponents can do.

41. Comparing the weights of NELSON (23 knots) and 16 B (27 knots), it is seen that NELSON is 1,500 less displacement, that the machinery weights are approximately the same and that a saving of about 2,20 tons is effected her protection weight for the same protection, neglecting her inclined belt.

It therefore appears that if it should prove possible to build a ship of the NELSON type, speed 27 knots, she could have 9-16” guns and approximately the same protection as 16 B.

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Alternatively, as far as weights are concerned, the adoption of NELSON design might permit each of the 27 knot ships t be increased to 30 knots.

42. The layout of the NELSON design is attractive from the material point of view in that the turrets are forward, the secondary and A/A armament amidships, and the aircraft aft, clear of blast. This principle appears to have been adopted in DUNKERQUE.

The well known disadvantages of NELSON, her lack of fire right aft and her unhandiness are not here discussed.

43. D.N.C. remarks as follows on NELSON design:-

“Although in the NELSON design an economy in protection weight was effected by grouping the main armament forward, it is considered that a similar economy will not result in a design required to carry the HA/LA armament, aircraft etc. proposed for the new Battle Cruiser.

Further it is unlikely that the machinery of a Battle cruiser can be satisfactorily accommodated if the three turrets are grouped forward.”

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CONCLUSION

44. Although conclusions regarding the effect of various guns on armour, as shown in the attached table, must be drawn with great caution, it is fair to say that the relative performance of the guns against belts is shown correctly. The information on which the performance of decks is based is scanty.

45. There are important factors which cannot be measured in an analysis of this nature or in a tabular statement.

In good visibility and with aircraft spotting, great damage can be done at long range, in which case the ship with a powerful armament and less protection may be at an advantage, and the decisive range, for which the better protected ship is designed, may never be reached.

A margin of protection of one ship over another may be entirely outweighed by the conditions of the battle, visibility, inclination, etc. It is dangerous to assume, except within very wide limits, that the fighting range can be dictated.

The size of gun

46. The problem may be considered as that of obtaining the correct balance between armament, protection and speed.

16 A and 14 D are examples of the two extremes of ill adjusted balance; in 16 A too powerful an armament is mounted with the result that the ship is very vulnerable, and 14 D is over protected for her armament.

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30 knots ship.

47. A 15” armament is not inferior to a 16” , because the former can have better protection, particularly decks, and she is better than the 16” ship for standing in the line against 16” fire.

The same remarks apply when comparing the 15” with the 12-14” 30 knot ship; the 15” is the better ship.

27 knot ship.

48. The superiority of the 16” ship over the 15’ is here more marked, because the zone during which her heavier fire can be brought to bear, before either ship’s protection fails, extends to a lower range. The 15” ship is still, however, better protected for standing in the line against 16” fire and against aircraft.

Similar remarks apply to the 12-14” ship as compared to the 15”, except that the 14” ‘zone of superior fire’ extends to still lower range, though, again the 15” ship is better protected for standing in the line against 16”

23 knots ship.

49. It has not been stated whether quadruple 15” turrets are possible or whether 12-15” could be mounted, but it appears unlikely.

9-15” in a 35000 ton 23 knot shp appears to be under gunned, since both the 9-16” and the 12-14” can be adequately protected.

The advantages of the 16” ship as compared to the 14” are that each hit has 1½ times the explosive effect, and, for the same protection, there is a zone of 3000 yds. during

——page break——

which the 16” can pierce the 14” ship’s belt, whilst her own is immune.

The 14” ship, on the other hand, may expect to obtain 4 hits to 3, and has therefore a better chance to hit some vital unprotected point at ranges above and below the zone where the 16” ship can pierce her belt. It is also sometimes urged that to hit is the important factor, whether with 14” or 16”, and the issue will depend largely on whether that hit is in a vital spot or not.

The difference between the 12-14” and 9-16” may not therefore be very great in the 23 knot ship of 35000 tons, but the advantages of the 16” are the more concrete.

Treaty considerations.

50. If the 14” gun should be the upper limit, and if our opponent has already some 15” ships of 30 knots, we could not build so powerful a 30 knot ship with 14” guns – but, apart from the value of speed, the 12-14” (14 F)ship of 27 knots should be of equivalent fighting power to the 15” 30 knots ship.

51. Within the present limitations, the ideal would appear to be:-

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T.D. Memo No 132
Aug 1935
ADM 1/9387

PROTECTION OF CAPITAL SHIPS

The Protection of capital ships is here examined to illustrate the sacrifice to be accepted if high speed is to be incorporated in the design.

2. It is generally accepted that we cannot afford the luxury of a Battle Cruiser which is unable to stand in the line. She must, in fact, be a fast Battleship. From this it follows that the Battle Cruiser, though perhaps of less gun power and less able to stand up to close range fire, must be as well protected as the battleship for closing to a reasonably effective range; until ascendency has been gained she may then have to use her speed to remain at an effective, but favourable range for herself.

Decisive Range

3. The Battle instructions, Clause 9 (g), state that a decisive range of between 12,000 and 16,000 yards will be aimed at and the reasons for this choice would appear to be as follows:-

4. Decisive actions only occur when both sides either wish to fight or when one or other cannot avoid action, in which case “fighting power” and not speed is the ultimate requirement. The decision may well depend finally on the morale and striking power of our fleet at short range; a range should therefore be chose which gives morale the greatest opportunity, where the rate of hitting is high and the factor of luck low, where the enemy (through short time of flight and large danger space) is least able to avoid punishment, but where our own ships are not liable to destruction by magazine explosions – by the lucky hit.

5. When the battle reaches this stage, air spotting and the primary control positions, with many of the refinements of fire control, ay well be out of action, having, it is to be hoped, contributed to gaining an ascendency during the earlier stages. Although air spotting can give effective hitting and perhaps even a decision, for the final destruction of the enemy we must be prepared to close to a range where direct spotting is possible in the confusion and smoke of battle, and where hits can be assured.

6. For these reasons, action ranges of 12,000 to 16,000 yards must be provided for in spite of the advance in air spotting and fire control, and the design of the modern and reconstructed ships permit them to fight at these approximate ranges against 14-inch fire.

Modern Protection.

7. The attached tables and graphs show that in the suggested 197 Battle Cruiser (35,000 tons) the armour belt is pierced by the 14” high velocity gun at a 2,500 yards higher range than in the 1937 Battleship (Design “Q” – 32,800 tons – 3 Quadruple 14” – 23 kts.), but that these ships are similar with regard to plunging fire and protection against bombs.

The 1937 Battleship, on the other hand, is inferior to NELSON in that her belt is pierced at a range 3,000 yards higher than in NELSON, who has also considerable advantage in deck protection. This is understood to be due to the economical distribution of the armour, inherent in the type of design and to the belt being inclined and inboard, which gives a more favourable striking angle for the armour and slightly reduces the area of the protected deck. The inclination fo the belt has, however, the possible disadvantage of deflecting shell to the ship’s bottom and may therefore be unacceptable in future design.

Closing the range.

8. As compared to NELSON, both the 1937 ships would be at a disadvantage against plunging fire of 14” guns between 29,000 and 26,000 yards. Hits at this range, though possibly rare owing to the long time of flight and small danger space, are most effective.

9. It may perhaps be said that the speed of the Battle Cruiser will permit her to close through this danger zone fairly quickly, and she would then be on even terms with NELSON (14”fire) as regards protection until she reaches 19,000 yards, when at 90º inclination her machinery compartments will be open to damage through the belt. If closing further without grave danger of vital damage she would have to rely on her speed to remain at a favourable inclination.

10. By comparison with the 1937 Battleship, the Battle Cruise would be equally protected until closing to 19,000 yards, when she would have to close through a 2,500 yards zone before the Battleship’s belt could be pierced at 90º inclination. Again, during this period, she would have to rely on her speed to remain at a favourable inclination.

Deck Protection.

11. The decks of both the 1937 ships would appear to be adequate against bombing, but the advantage in NELSON against plunging fire is important. With air spotting, hits between 29,000 and 26,000 yards are practicable, particularly when direct laying and training are possible.

To provide the Battle Cruiser with reasonable certainty of being able to reach an effective range, it would seem essential that no sacrifice be made in deck protection. This principle has been accepted in the 1937 Battle Cruiser by comparison with the 1937 Battleship, but it is desirable that both these ships should more nearly approach the NELSON standard against plunging fire.

The balance between armament, protection and speed.

12. It is not here proposed to examine in detail the value of speed by comparison with fighting power, but three points would appear to be outstanding:-

(i) In the event of a decisive action developing (para. 4. above) ‘fighting power’ will ultimately be the main requirement of capital ships.
(ii) Fast capital ships might be required to deal with similar foreign ships, not so much in a major fleet action, but rather when detached on harassing operations.
(iii) What is suitable against one country may not be the best construction when considering another possible enemy, e.g., Battle Cruisers would be of less importance against Japan than against European powers who are building this type of ship; in fact, against Japan, the sacrifice of fighting power in the battle fleet resulting from building Battle Cruisers may be most undesirable at present.

13. Assuming that it be decided that strategically and on the grounds of morale and prestige, a proportion of fast capital ships is an immediate requirement, and that it is probably that corresponding foreign ships will attain 30 knots, it is for consideration what is the minimum speed we can accept, having regard to the gain in fighting power resulting from a lower speed.

14. War experience suggests that, where speeds are comparable, the strategic and tactical considerations have a greater influence on bringing a superior force to bear at the decisive time and place than has the ability to develop equal or even, within limits, a greater speed.

15. With this in mind, and considering the fleet as a whole, with its fighting power and reconnaissance forces, it is suggested that we should deliberately accept a lower speed, say 27 or 28 knots, if investigation shows the resulting gain in fighting power to be worth while.

16. This difference in maximum speed will have but little effect in the plane of strategy; such factors as the position of bases, intelligence, reconnaissance, plan and disposition of forces, will generally outweigh the practical effect of a margin of 3 knots on one side.

17. Tactically it must be our utmost endeavour to bring superior reconnaissance to bear and the development of air reconnaissance to some extent reduces the value of superior speed, in that greater opportunities are afforded for gaining that position which should ensure interception even if our speed is slightly inferior. Interception having been effected, Fighting Power is the main requirement.

CONCLUSION

18. The figure, 3 knots less speed, cannot at present be supported by detailed argument and data, and it is suggested that D. of N. Might examine a number of typical situations to test the validity of the proposal.

19. It is further proposed that D.N.C. should examine the gain in fighting power (i.e., armament or deck protection of armour belt), which could be expected if a reduction of 3 knots in the Battle Cruiser were accepted.

20. Underwater protection is a separate problem and is not here examined the main development being the greatly increased watertight subdivision, which also limits damage by gunfire and has a bearing on the belt and deck protection.

21. Previous investigations into the protection of capital ships are included in “The Characteristics of the Battleship – Staff paper, June 1933” – which this paper summarises and brings up to date. These past examinations have illustrated that if the principle of “corresponding protection” be departed from, and ill balanced ship is likely to result – i.e., a 14-inch gun ship, protected against 16-inch fire, is unduly large for her gun power.

22. If it be decided to increase the protection of the Battle Cruiser with sacrifice of speed, the decision whether it should be applied to the deck or belt will be influenced by the distribution of armour and the virtual target presented at various ranges, a matter for detailed investigation; but it would appear from para. 11 above the improvement of the deck protection is the more important.

It must be recalled that the use of inclination may assist side armour, but no such measure can assist the deck to resist bombs.

August, 1935.

(T.D. Memo. No. 132.)

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(Appendix to T.D. Memo. No. 132.)

PROTECTION OF CAPITAL SHIPS.

The following information is added to the Memorandum to facilitate a decision on the points raised by A.C.N.S. This Appendix summarises recent discussions on the Staff Paper “The Characteristics of the 1937 Battleship” compiled in 1933.

2. Decisive Range and Speed.

These points are remarked on by A.C.N.S., and in the Memorandum, and D. of N. has been requested to examine the possible implications on the proposal to reduce the speed.

3. Protection against Gunfire.

A fast ship fighting against slower ships can use her speed in some measure to dictate the range and to place her side armour at a favourable inclination.

On the other hand, no manoeuvre of this sort can assist her deck armour to resist plunging fire – except in so far as turrets and other obstructions reduce the deck target at fine inclinations.

4. Protection against Bombs.

Even if the “B” Bomb should replace other bombs for sea service powerful deck armour is still required for defence in harbour.

High bombing, though much less likely to hit than Dive Bombing, has greater penetrating effect.

Decks which protect against High Bombing above 5000 feet will keep out the same bomb used with Dive Bombing.

As with plunging fire, nothing we can do in the way of manoeuvre can assist the deck to resist a hit by a bomb.

The percentage of hits with unseen High Bombing may be as high as 15%, but if seen the long range A.A. fire goes far to meet the menace.

The 2000 lb. Bomb is possible, but it is far more likely that attackers would prefer to use numbers of smaller bombs than a few of 2000 lbs. It is not likely that Dive Bombing will be practicable with more than 1000 lb. bombs.

5. Magazines and Engine Rooms v. Bombs.

It has been held that magazines must be protected against the largest bomb reasonably likely to be used, but for the machinery spaces les protection must be accepted, reliance being placed upon the sub-division of the ship.

In the recent tentative Battleship designs, the magazines were protected against the 1000 lb. Bomb up to 12000 ft., and the machinery spaces against the 500 lb. Bomb, which it is though is the probable sea service bomb.

6. The question is – are we allowing for sufficient weight of Bomb, particularly for magazines?

The following table show the protection value of various decks.

10000 to 12000 ft. is regarded as a reasonable Bombing height.

Heights above which the deck will be perforated.


Deck.

2000 lb.
A.P. Bomb.
ft.

1000 lb.
A.P. Bomb.
ft.

500 lb.
S.A.P. Bomb.
ft.

4”

3000

7000

12000

5”

5000

10500

Immune

6”

7000

10500

- do -

7”

9000

Immune

- do -

7. Under Water Attack.

It does not appear likely, though it is possible, that a warhead of more than 750 lbs. will be developed for use from destroyers, submarines and aircraft.

To use weight for bulge and other protection against a large warhead in contact would seem waste of effort when the most probable form of attack will be the contact-non-contact pistol and “B” Bomb under the bottom – against which W.T. sub-division of the ship is the only defence. We must at present accept the possibility of a main compartment being flooded in this way.

8. W.T. Sub-division.

The W.T. Sub-division forced on us by the “non-contact” threat, and facilitated by modern machinery design, has an important bearing on the isolation of damage by gunfire or bombs except for the magazines.

It is for consideration how far this sub-division permits us to accept less protection for important compartments other than magazines, for the sake of offensive power.

T.D.
16.8.35

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T.D. Memo No 136
Sep 1935
ADM 1/9387

 

CAPITAL SHIPS

CALIBRE OF GUNS
AND PROTECTION

Tactical Division
    Naval Staff.
      (T.D. Memo. No. 136)
        September, 1935.

CAPITAL SHIPS.

CALIBRE OF GUNS.

To decide the calibre of the gun it is first necessary to investigate the effect of various mountings on the other two main characteristics of the ship – PROTECTION and SPEED – if a proper balance between offence and defence is to be reached. “Defence” is a somewhat misleading term as applied to armour protection against gunfire; for, in circumstances where it enables our guns to reach the vitals of the enemy before his can reach our vitals, armour is by no means a purely passive defence – it secures our offensive.

2. It is generally accepted that a capital Ship, whether Battleship or Battle Cruiser, must be sufficiently powerful to contribute effectively in the battle line, and to withstand aircraft and torpedo attack so far as possible. It is only necessary at this stage to examine the protection in general terms, the detailed distribution being decided upon later.

3. The outline designs have been analysed in the attached tabular statement after consultation with D.N.C., and the examination is here made purely fro the fighting point of view without other treaty considerations than a displacement limit of 35000 tons.

4. It is assumed that the maximum displacement must be 35000 tons, and the problem is examined below under the following main headings.

Comparison of guns.

The 30 knot ship.

The 27 knot ship.

The 23 knot ship.

NELSON Design.

The General Problem.

5. To clear the issue the following general conclusions resulting from the investigation are outlined below:-

(i) For a given displacement and speed there appears to be a correct balance of armament and protection, and, in the faster ships it seems that this can generally be attained by one of two calibres of gun separated by not more than 1 inch. The extra protection possible with the smaller gun compensates for the superior hitting power of the larger gun.

(ii) A slower ship of the same displacement can be so well protected that no additional protection can usefully be added as a result of mounting the smaller gun. The problem is then that of estimating the value of more numerous and smaller guns, as compared with fewer heavier guns, in their shattering effect before decisive range is reached.

(iii) Unless the ship with the light gun is adequately protected against the heavier gun, the advantage she gains by greater numbers is outweighed by the vulnerability of her vitals.

(iv) It appears that neither 9-16” nor 12-14” can be mounted in a 30 knot ship with sufficient protection.

(v) A well balanced 30 knot 15” ship can be designed which is a match for the ships mentioned in (iv) and which is better able to stand in the line.

(vi) At 27 knots there is no great difference between the 16” and 15” ships, and they are both superior to the 14”

(vii) For a 23 knot ship the 16” gun seems undoubtedly the best unless 12-15” or 12-14” can be mounted. The more numerous guns might tell at medium or long ranges, but the 16” would be greatly superior at decisive ranges.

The inclusion of four turrets congests the design.

(viii) If a new limit of displacement be assumed, it is not justifiable to draw conclusions from the following analysis.

6. The Tabular Statement

The graph shows the approximate performance of the belt against 16”, 15” and 14” fire. The lower the lines on the graph the better is the belt protection.

The approximate ranges at which the decks are penetrated by 16” plunging fire are also shown on the graph. In this case, the higher the spots on the graph the better the deck protection.

The value of the decks against bombs is estimated in the bottom table.

7. Decisive Range.

On T.D. 151/35 (Protection of Capital Ships), it was suggested that in spite of the advance of Air Spotting and Fire Control, Capital Ships must still be designed to fight at between 12000 and 16000 yds, as it may well be necessary to close to a range where direct spotting is possible in the smoke and confusion of battle, with, perhaps, air spotting and many of the refinements of fire control out of action.

In these remarks, therefore, the term “ Decisive Range” is used to indicate ranges from 12000 to 15000 yds., which are those given in the Battle Instructions; and the term “Battleship Protection” implies that the vitals are protected at these approximate ranges.

8. The value of speed as protection during action.

A superiority of speed if sufficient, is of undoubted tactical value in certain circumstances to enable an action to be forced or to be avoided.

The statement, however, that speed can afford protection in action is only true to a limited extent and may be misleading. Speed has a value for protection in Capital Ships in so far as it enables the fighting range to be dictated but this does not apply when the margin of speed is mall, or in low visibility.

It is also sometimes said that the fast ship can use her speed to keep her armour at favourable inclination, and thus increase its protective value.

It is very open to question whether, in the uncertainties and varying conditions of contact and battle, the fast ship could in fact dictate the range or the inclination of her armour except perhaps when fighting a ship very considerably slower than herself. The value of speed purely as protection in battle cannot therefore be relied upon.

COMPARISON OF GUNS.

9. The considered below are:-

NELSON’s 16”
American 14” H.V.
British new 15” (estimated).

These guns are considered typical of modern attack and, if the ship is to stand in the line, smaller guns need not be considered (see note to attached tables).

The Italian 15” is reported to have an abnormally high M.V., but it is understood to be unlikely that its striking energy will exceed that of the new British 15”.

10. The factors to be considered in the comparison of guns are shown in the following table:-

 

14” guns.

15” guns.

16” guns.

Weight of shell

1590 lbs.

1938 lbs.

2375 lbs.

Weight of burster

49 lbs.

48.5 lbs.

59.5 lbs.

20,000 yds – Time of flight.

31 secs.

30.5 secs.

30 secs.

20,000 yds - Danger space of 30 ft. target

35 yds.

35 yds.

35 yds.

Loading interval.

Details not available; with similar turret designs there will be little or no difference in rate of fire.

Maximum range.

Sufficient in all cases.

11. It is evident from the above that “Hitting Power”, as affected by striking energy and the explosive power of the shell, and “Chance of Hitting”, as affected by the number of guns per salvo, are the important factors. It is therefore the basis that the comparison is made below; rate of fire time of flight, etc., are not taken into account.

Hitting Power.

12. The means by which gunfire can reduce the fighting efficiency of an opponent are:-

(a) By penetrating the vitals through the armour protection.
(b) By shattering the “soft ends”, bridges and fire control positions.

13. For penetrating the vitals it is evident that, against equal protection, the larger gun has the advantage, whether through the belt or the deck.

14. The shattering effect may be of particular importance when fighting at ranges at which neither ship’s armour can be pierced; in these circumstances, the smaller, more numerous guns should hit more often, but this must be weighed against the extra explosive power of her opponents’ larger shell and the advantage she has in penetration.

Chance of Hitting.

15. It is here assumed that an increase in the number of guns per salvo results in a proportional increase in the hits to be expected. The exact truth of this assumption in practice is perhaps open to doubt, but it is a fact that the chance of hitting is improved by the extra rounds “packing the salvo” to some extent, and by the fact that the increased spread ay enable the target to be found and held more readily.

16. For the number of guns here considered (4 to 6 guns per salvo) this assumption may give an unduly favourable view of the more numerous guns.

The heavy gun is widely favoured in our Service, but it must be recognised that both size and number of guns are important considerations. The assumption made in para. 15 above has therefore been accepted in order to give full weight to the argument for the more numerous armament.

17. In the comparison of fighting power, as represented by gun power, protection and speed, on the basis of the attached tabular statement, it is realised that conclusions must be drawn with caution. The figures used cannot be taken as exact, particularly with regard to Deck Protection.


The 30 Knot Ship.

18. The following assumptions are made:-

(i) Maximum Displacement – 35,000 tons.
(ii) Speed 30 knots.
(iii) A minimum of 8 main armament guns.
(iv) Only three turrets.
(v) At least one turret must be able to fire aft, and NELSON design cannot therefore be adopted.

Designs 14C & 16A

19. These ships are vulnerable to vital damage by 16” & 15” through their belts considerably outside decisive range; they are not well protected against 14”, and their machinery compartments are unduly open to plunging fire and bombs, particularly 16A within her 3” deck.

20. It might appear that 14C would have some advantage in the shattering effect of her 12 guns upon unprotected parts. According to the assumption made in paragraph 15 she might expect to obtain 4 hits to every 3 scored against her by the 16” ship, but this advantage must be balanced against the explosive effect of individual 16” hits, which is 1½ times that of a 14”, and against the considerable extra penetrative power of the 16” shell.

21. Both these ships are considered to be over gunned for 30 knot ships of 35,000 tons; it will be seen from the comparisons made below that they are too lightly protected to stand up against other 30 knot Battle Cruisers shown in the table, and that they could not contribute effectively in the Battle line without grave risk of damage

Designs 14E & 15A

22. These 30 knot ships have similar protection except that the machinery deck of 15A is weaker than that of 14E by about 3,000 yards against 16” plunging fire.

Neither ship could stand in the battle line at decisive range without grave risk, but they could contribute usefully at about 19,000 yards against 16” and 15” fire.

Against each other, 15A appears the better shp; she has the greater hitting power her protection against 14” is better than that of 14E against 16”, and her 9-15” would compare favourably in all respects with her opponents 10-14”.

In the comparisons made below it will be seen that 15A in spite of her somewhat weaker machinery deck is also better than 14E for fighting against other ships or when standing in the line, because of the superior hitting power of her 15: guns.

Design 14D.

23. Although her protection is good, this ship is considered to be under gunned, whether with 8-14” or 6-16”. Six 16” guns would not be satisfactory from the fire control point of view, and reference to the table shows that the 14” has inadequate hitting power against eh protection which can be provided in a 30 knot ship of greater gun power than 8-14” (i.e. 15A or 14E).

This ship is not further considered in this analysis.

Comparison between 15A and 14C.

24. The 15” guns should reach the vitals of 14C through her belt at about 19,000 yards whilst her own belt should hold against 14C’s 14” fire down to about 15,000 yards; 15A’s decks are considerably superior to those of 14C.

These advantages, together with the extra explosive power in the 15” shell, are considered to outweigh the superior volume of fire from the 12-14” guns of 14C, which it is assumed would give 4 hits to every 3 obtained by the 9-15”.

Comparison between 15A and 16A

25. The 15” guns should reach the vitals of 16A through the belt slightly before her own are vulnerable to 16” fire, and the 15” plunging fire should pierce 16A’s machinery deck at about 21,000 yards whilst her own decks hold out 16” fire up to 25,000 yards.

Taking into consideration the extra explosive power of the 16 inch shell, there seems little to choose between these ships when fighting against each other. But if both ships had to stand in the battle line against 16” or 15” fire, 15A’s belt would have an advantage of about 2,500 yards, and her decks 3,000 yards. 15A is also better against air attack.

On the whole therefore, owing to 15A’s comparatively light protection, particularly the machinery deck, 15A is considered the better balanced ship.

Note. 14E, with her 10-14” and similar protection to 15A, does not compare so favourably with 16A, whose 16” shell can pierce 14E’s belt at 18500 i.e.1,000 yards before her own belt is vulnerable to 14” fire.

26. Protection against bombs.

This problem is not here examined in detail, but it has a bearing on the decision regarding the calibre of gun to be mounted, because it affects the weight available for the armament.

The Decks required against plunging fire are comparable with those required against bombs; it would appear that the Deck protection should be of the order of that in 14D or E and that, on both grounds the plunging fire or bombs 14C and 16A have not sufficient Deck protection.

27. The 30 knot ship – Conclusions.

(i) 14” guns.

All ships, except 14C and 16A can be well protected against 14” fire.

Except when the armament is greatly reduced as in 14D, the 15” and 16” guns can reach the vitals of a 14” ship before her 14” guns can penetrate the protection of the more heavily gunned vessels.

It appears, therefore, that the 14” gun should be ruled out unless required by treaty.

(ii) 16” guns.

16” guns cannot be mounted in a 30 knot ship with adequate protection (16A); such a ship could not be expected to stand in the Battle line without grave danger of vital damage.

(iii) 15” guns.

The 15” gun can be mounted in a comparatively well protected ship (15A), who has good Decks and whose Belt would permit her to close against 16” fire to about 19,000 yards. The 30 knot 15” ship would incur grave risk at Decisive Ranges, but she is able to contribute effectively in the battle line at useful ranges and would, individually, be a match for any 30 knot 16” or 14” ship of 35,000 tons.

The conclusion is reached that the 15” gun is the best armament for a 30 knot ship of 35,000 tons displacement.


THE 27 KNOT SHIP.

28. The effect on armament and protection of a 3 knot reduction in speed is shown in designs 14F, 15B, 16B and 16C.

The strategical and tactical effect of this reduction is under discussion in T.B.151/35.

The arguments against such a reduction are self-evident, but the advocates of the slower ship urge that the resulting gain in fighting power may well outweigh the disadvantage of the slower speed. It is suggested that decisive battles do not occur as a result of slightly superior or equal speed of capital ships; an unwilling enemy with freedom of movement can generally avoid action unless strategic factors, or our “position”, gained by reconnaissance and the use of all arms of the fleet, force him to fight.

If our opponent should build 27 knot ships whilst we build 30 knot ships, we should be at a disadvantage in that, although our speed might enable us to overtake the enemy we would be of less fighting power.

29. The 27 knot designs examined are:-

(I) Design 14 F.

12-14”, protection similar to 14E. with slightly inferior decks 0 speed 27 knots.

(II) Design 15 B.

9-15”, Battleship protection as in 14D, speed 27 knots.

(III) Design 16 B.

8-16”, Battleship protection as in 14C, speed 27 knots. The arrangement of 2 Triple and one pair gun turret is not satisfactory and this ship is not here examined in detail.

(IV) Design 16 C.

9-16”, protection as in 14 E, speed 27 knots. This design is an estimation only, derived from the weights given for 16 B and 16 A.

30. Comparison is here made purely on the basis of fighting power in order to assess the gain resulting from a sacrifice of 3 knots; and this margin was chosen as that which, whilst enabling an addition of fighting power, si insufficient to permit the faster ship to dictate the fighting range with any certainty – if strategical, tactical or weather conditions should force her to fight.

31. It has been suggested above that 16 A, and 15 A, are the best 30 knot ships, and the 27 knot ships (14 F, 15 B, 16 B and 16 C) are therefore compared with these.

Comparison of 14 F (27 knots) with 16 A or 15 A (30 knots).

32. It is difficult to assess the comparative fighting value of 14 F with 16 A or 15 A.

As compared to 16 A, 14 F, has a valuable superiority in deck protection.

She should obtain 4 14” hits at useful ranges to every 3 16” hits by her opponent. 16 A would gain an advantage at 18,500 yards, by being able to pierce 14 F’s belt 1,000 yards before 14” guns can reach 16 A’s vitals. 14 F would b better able to stand in the line than 16 A.

Against 15 A, similar remarks apply, except that 14 F has not in this case so great an advantage in deck protection, but she is able to close to a more effective range for bringing her high volume of fire to bear.

It would appear that 14 F is as powerful as 16 A or 15 A, and she has an asset in her good decks and Torpedo bulkhead.

Comparison between 15 B (27 knots) and 16 A or 15 A (30 knots).

33. Against 16 A, 15 B has a 2,500 yard advantage in belt protection and greatly superior decks.

Against 15 A she is about equal when between ranges of 27,000 and 17,500, when neither ship’s vitals are vulnerable. 15 B, having better decks and belts is more able to withstand air attack and to close to decisive range.

Comparison between 16 C (27 knots) and 16 A r 15 A (30 knots).

34. The same method of comparison shows that 16 C is of definitely superior fighting power to 16 A or 15 A.

Comparison between 15 B (27 knots) and 16 C (27 knots).

35. When fighting against each other the protection of 15 B against 16” fire is about the same as that of 16 C against 15”; and there is little to choose between the two ships other than the superior explosive effect of the 16 inch against unprotected parts, and the somewhat better protection of 15 B against bombs.

If both ships were in the line against Battleships, again there is little to choose because, although the armament of 16 C has a greater shattering effect, the protection of 15 B enables her to close to 17,000 yards for decisive results (2,000 yards closer than 16 C could close without serious risk). 16 C would also be slightly more vulnerable to plunging fire, and her torpedo bulkhead is lighter than that of 15 B.

36. These considerations lead to the conclusion that a well balanced 27 knot ship can be built, either with 9-16”, 9-15: or 12-14”. For fighting against battle cruisers 16C (9-16”) is probably the best, but 15 B may be considered the better general service ship, because she can contribute in the battle line better than the 16” or 14” ships, and she will be a good match for any battle cruiser.

THE 23 KNOT SHIP.

37. From the figures given for NELSON, 14 Q and 16 A, it appears that a 9-16” ship could be designed with one turret aft, and that she might have full Battleship protection as in 15 B.

38. To mount 15” guns in this ship would be of little use unless a considerable increase in numbers were possible, and it appears unlikely that 12-15’ could be included. The protection is already adequate, so the weight saved by mounting 9-15” would only be employed in a reduction of displacement.

39. A 12-14” gun ship would gain in the number of hits over a wide and useful zone down to about 17,000 yards, when 16” guns could pierce her vitals. No definite conclusion can be drawn in this respect, but it appears that the extra hitting power of the 16 inch, combined with its penetrative power at decisive range, would tip the balance in favour of the larger gun.

NELSON DESIGN.

40. Although it is not desired to re-open detailed discussion on this design, it is necessary to examine the effect on the armament if adopted, if only to see what our opponents can do.

41. Comparing the weights of NELSON (23 knots) and 16 B (27 knots), it is seen that NELSON is 1,500 less displacement, that the machinery weights are approximately the same and that a saving of about 2,20 tons is effected her protection weight for the same protection, neglecting her inclined belt.

It therefore appears that if it should prove possible to build a ship of the NELSON type, speed 27 knots, she could have 9-16” guns and approximately the same protection as 16 B.

Alternatively, as far as weights are concerned, the adoption of NELSON design might permit each of the 27 knot ships t be increased to 30 knots.

42. The layout of the NELSON design is attractive from the material point of view in that the turrets are forward, the secondary and A/A armament amidships, and the aircraft aft, clear of blast. This principle appears to have been adopted in DUNKERQUE.

The well known disadvantages of NELSON, her lack of fire right aft and her unhandiness are not here discussed.

43. D.N.C. remarks as follows on NELSON design:-

“Although in the NELSON design an economy in protection weight was effected by grouping the main armament forward, it is considered that a similar economy will not result in a design required to carry the HA/LA armament, aircraft etc. proposed for the new Battle Cruiser.

Further it is unlikely that the machinery of a Battle cruiser can be satisfactorily accommodated if the three turrets are grouped forward.”

CONCLUSION

44. Although conclusions regarding the effect of various guns on armour, as shown in the attached table, must be drawn with great caution, it is fair to say that the relative performance of the guns against belts is shown correctly. The information on which the performance of decks is based is scanty.

45. There are important factors which cannot be measured in an analysis of this nature or in a tabular statement.

In good visibility and with aircraft spotting, great damage can be done at long range, in which case the ship with a powerful armament and less protection may be at an advantage, and the decisive range, for which the better protected ship is designed, may never be reached.

A margin of protection of one ship over another may be entirely outweighed by the conditions of the battle, visibility, inclination, etc. It is dangerous to assume, except within very wide limits, that the fighting range can be dictated.

The size of gun

46. The problem may be considered as that of obtaining the correct balance between armament, protection and speed.

16 A and 14 D are examples of the two extremes of ill adjusted balance; in 16 A too powerful an armament is mounted with the result that the ship is very vulnerable, and 14 D is over protected for her armament.

30 knots ship.

47. A 15” armament is not inferior to a 16” , because the former can have better protection, particularly decks, and she is better than the 16” ship for standing in the line against 16” fire.

The same remarks apply when comparing the 15” with the 12-14” 30 knot ship; the 15” is the better ship.

27 knot ship.

48. The superiority of the 16” ship over the 15’ is here more marked, because the zone during which her heavier fire can be brought to bear, before either ship’s protection fails, extends to a lower range. The 15” ship is still, however, better protected for standing in the line against 16” fire and against aircraft.

Similar remarks apply to the 12-14” ship as compared to the 15”, except that the 14” ‘zone of superior fire’ extends to still lower range, though, again the 15” ship is better protected for standing in the line against 16”

23 knots ship.

49. It has not been stated whether quadruple 15” turrets are possible or whether 12-15” could be mounted, but it appears unlikely.

9-15” in a 35000 ton 23 knot shp appears to be under gunned, since both the 9-16” and the 12-14” can be adequately protected.

The advantages of the 16” ship as compared to the 14” are that each hit has 1½ times the explosive effect, and, for the same protection, there is a zone of 3000 yds. during which the 16” can pierce the 14” ship’s belt, whilst her own is immune.

The 14” ship, on the other hand, may expect to obtain 4 hits to 3, and has therefore a better chance to hit some vital unprotected point at ranges above and below the zone where the 16” ship can pierce her belt. It is also sometimes urged that to hit is the important factor, whether with 14” or 16”, and the issue will depend largely on whether that hit is in a vital spot or not.

The difference between the 12-14” and 9-16” may not therefore be very great in the 23 knot ship of 35000 tons, but the advantages of the 16” are the more concrete.

Treaty considerations.

50. If the 14” gun should be the upper limit, and if our opponent has already some 15” ships of 30 knots, we could not build so powerful a 30 knot ship with 14” guns – but, apart from the value of speed, the 12-14” (14 F) ship of 27 knots should be of equivalent fighting power to the 15” 30 knots ship.

51. Within the present limitations, the ideal would appear to be:-

(a) The 15” gun for the 30 knots ship.
(b) The 15” or 16” for the 27 knot ship, though the 15” ship may be preferred because she could stand in the line better and has somewhat stronger decks.
(c) The 16” or 15” for the 23 knot ship, if, as is assumed, 12-15” cannot be mounted.

Accompanying Graphics
Click on the following to view enlarged versions

H.M.S. Nelson Class Armour Efficiency Against 16inch Attack    H.M.S. Nelson Class Armour Efficiency Against 14inch H.V. Attack    H.M.S. Nelson Class Armour Efficiency Against 14inch M.V. Attack
Above- H.M.S. Nelson Class Armour Efficiency Diagrams

H.M.S. Queen Elizabeth Class Armour Efficiency Against 16inch Attack    H.M.S. Queen Elizabeth Class Armour Efficiency Against 14inch H.V. Attack    H.M.S. Queen Elizabeth Class Armour Efficiency Against 14inch M.V. Attack
Above- H.M.S. Queen Elizabeth Class Armour Efficiency Diagrams

H.M.S. Barham Armour Efficiency Against 16inch Attack    H.M.S. Barham Armour Efficiency Against 14inch H.V. Attack    H.M.S. Barham Armour Efficiency Against 14inch M.V. Attack
Above- H.M.S. Barham Armour Efficiency Diagrams

H.M.S. Royal Sovereign Class Armour Efficiency Against 16inch Attack    H.M.S. Royal Sovereign Class Armour Efficiency Against 14inch H.V. Attack    H.M.S. Royal Sovereign Class Armour Efficiency Against 14inch M.V. Attack
Above- H.M.S. Royal Sovereign Class Armour Efficiency Diagrams

US Navy Classes Armour Efficiency Against 16inch Attack    US Navy Classes Armour Efficiency Against 15inch Attack
Above- United States Battleships Maryland, California, New Mexico & Pennsylvania Classes Armour Efficiency Diagrams

Japanese Classes Armour Efficiency Against 16inch Attack    Japanese Classes Armour Efficiency Against 15inch Attack
Above- Japanese Mutsu, Ise & Fuso Classes Armour Efficiency Diagrams

H.M.S. Hood Armour Efficiency Against 16inch Attack    H.M.S. Hood Armour Efficiency Against 14inch H.V. Attack    H.M.S. Hood Armour Efficiency Against 14inch M.V. Attack
Above- H.M.S. Hood Armour Efficiency Diagrams

H.M.S. Repulse Armour Efficiency Against 16inch Attack    H.M.S. Repulse Armour Efficiency Against 14inch H.V. Attack    H.M.S. Repulse Armour Efficiency Against 14inch M.V. Attack
Above- H.M.S. Repulse Armour Efficiency Diagrams

H.M.S. Renown Armour Efficiency Against 16inch Attack    H.M.S. Renown Armour Efficiency Against 14inch H.V. Attack
Above- H.M.S. Renown Armour Efficiency Diagrams

Capital Ship Design (top)    Capital Ship Design (middle)    Capital Ship Design (bottom)
Above- Capital Ship Designs Diagram (divided into three images- left is top of diagram, centre is middle and right is bottom of diagram).

END OF TRANSCRIPTION