REFERENCE DOCUMENTS & RESOURCES - OFFICIAL ADMIRALTY DOCUMENTS
ADM 186/251: PROGRESS IN GUNNERY MATERIAL, 1921
Updated 18-Oct-2007

This document is a modern transcription of a portion of Admiralty record ADM 186/251. It highlights the state of Royal Navy warship gunnery during the years 1922 and 1923. 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. This document is not complete. We shall endeavour to add additional portions as time permits.

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START OF TRANSCRIPTION

PROGRESS IN GUNNERY MATERIAL, 1921.

CONTENTS

  Section 1.- Fire Control Instruments.  
Article.   Page.
1. Dreyer table fitted in H.M.S. “ Hood ”- Gyro director training gear for Light Cruisers 9
2. Langley Automatic Inclinator 9
3. Rangefinders. Rangefinder trials at Fort Cumberland – 30 ft. Rangefinder – 30 ft. Rangefinder Mountings – Rangefinders in Light Cruisers and T.B.D.s – Bennet type Barr and Stroud Rangefinder instruction device – Rangefinder periscopes – Future design of Rangefinder Mountings 9
  Section II.- Sights and Sighting.  
4. Gunsighting telescopes – Comparison between German and British telescopes – Watertightness of Gunsighting telescopes – Binocular eyepieces for Gunsighting telescopes 11
  Section III.-Director Firing.  
5. Henderson’s director layer’s telescope 12
6. Gyro turret training gear 17
7. Local director sights 17
8. Director control tower 18
9. Carlake’s auto synchronous transmission gear 19
10. Gyroscopes for vertical datum line (Dr. Gray’s) 20
11. Cross levelling gear 21
  Section IV.- Progress in External Ballistics  
12. Computation of range tables 22
13. Motion of projectile in flight. Theoretical results of the trials carried out at Portsmouth in 1918 and 1919 23
14. The principal problem – The initial disturbance 23
15. Resistance of the air – Wind channel 23
16. Grain Island range 24
17. Allowance for Meteorological conditions – Experiments are about to be carried out in H.M.S. “ Canterbury ” 24
18. Allowance for rotation of the earth (Mr. Gallop’s formulae) 24
19.
Photographic range at the National Physical laboratory		 24
20. Loss of M.V. with wear 24
21. Ballistics of Projectiles – Difference in M.V. of different projectiles – Re-determination of ballistics for revision of range tables – Future Policy – Shape of head of projectile – Manufacturing tolerances – Reduced clearances – Rifled shell and hyper-velocity guns 24
22. Experimental range equipment – Solenoid Chronograph – Recording velocities on board a ship 27
23. Angle of departure – Origin of trajectory in undisturbed air and actual M.V. – Causes of gun dispersion – Empirical ballistic relations 28
24. Rapid cinematograph apparatus 29
25. The Solenoid experiment of July, 1919 – Calibration – Naval range 29
26. Trial of simultaneous firing and results 29
27. Consequences of coppering and rusty bore 30
27a. Foreign progress – German guns 30

(C458) Wt.11059/Pk3861 10/21 300 Harrow (Gp. 1) 112

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  Section V.- Guns and Gun Design.  
Article.   Page.
28. Auto-frettage system of gun construction 31
29. Super-velocity guns – the Delamare-Maze Turbine gun 31
30. Rifling and driving bands 31
31. Reduction in wear of guns, lubrication of bore – Decoppering – Ovality of wear 31
32. Comparison between British and German gun designs – New designs of guns 32
33. Recent gun accidents – Premature in 15 in. Mark I – Previous accidents 35
  Section VI.- Breech Mechanisms.  
34. Future heavy and medium mechanisms – Recent breech mechanism defects – Box slide K. modification 37
  Section VII.- Power Worked Gun Mountings.  
35. “ Baden’s ” 38 cm. turret – Use of electric power and hydraulic power self-contained in turret – Direct hoist from handling room to gun-house – Loading wagon in gun-house – Simultaneous loading – Anti-flash arrangements in handling room – Auxiliary loading chamber – Use of brass cylinder for charge and size of charge. 38
36. Points of detail of interest – Transporters in magazine and handing room – Shell grabs – Use of wire woven bands for lifting shell – Embarking arrangements – Floor plating – Working of main cage lever and interlocks - Chain and telescopic rammer – Jointing – The breech mechanism – The sights – Air blast arrangements – Stowage of spanners – Lubrication 40
37. Loading trials in “ Baden’s ” 38 cm. turret 42
38. Flash trials carried out in “ Baden ” 43
  Section VIII.- Transferable Gun Mountings  
  No further progress to report at present 45
  Section IX.- Anti-Submarine Weapons.  
39.
Stick Bombs – Hydrostatic fuzes – Gas checks for stick bombs – howitzer shells		 46
  Section X.- Projectiles  
40. Production of A.P.C. shells – Improvements in A.P.C. shells 13.5 in. and above – Trials to determine best weight (W/D3) for future shells of heavy guns 46
41. Performance of large A.P.C. shells at calibre plates 47
41a. Armour piercing quality of shells 48
42. Proof of shells – Outfits of shells for turret guns – Size of armour plates used for shell trials or proofs – Unsteadiness of shells at plate proof – 7.5 in., 6 in., and 5.5 in. shells – Shells 4.7 in. and below – For attack of ships – For attack of submarines – Outfits of 4.7 in. and below – Future lines of progress 48
43. Utility of A.P. Caps – Velocity for “ Cap Action ” 51
44. Rifled shells in connection with “ hyper-velocity ” guns 51
45. Variations in weight of shells in supply 52
45a.
Fillings for shells – Lyddite – Powder fillings – Effects of moisture in shellite		 52
46. Liability of shells to explosion or detonation in action 53
47. Chemical fillings for Naval shells – anti-ship shells – Gas cloud shells – Gas experimental station – Smoke cloud shells 54
48.
Ballistic caps – Conversion of existing shells to longer c.r.h. contour – Ballistic trials with long caps – Ballistic caps on H.E. shells		 55
49. Accidents with shells and precaution to be taken – Cracking of shells – “ Lord Clive ” accident 55
50. Target shells – Diving shells – Target smoke shell 56
51. Star shell 57
  Section XA.- Aerial Bombs.  
52. Aerial Bombs – Flame Bombs 57

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  Section XB.- Armour  
Article.   Page.
53. Preliminary remarks – Existing specification tests for armour – German K.C. armour – Trials for new armour specifications – “ Limiting velocities ” of holding K.C. armour at normal are increased – Proof plates – Deck armour – Roof plate butts – Splinter proof protection. 58
54. Tests of protection to be used in New Ship designs 60
  Section XI.- Propellants.  
55. R.D.B. Cordite – Ardeer cordite – Oval cordite – Tubular cordite 61
  Section XII.- Fuzes, Tubes, Primers, and Tracers.  
56. Policy in respect of fuzes to be supplied in future 61
57. Base percussion fuzes – No. 12 fuze – No. 15 fuze – No. 16 fuze 62
58. Direct action impact fuzes – No. 18 fuze 63
59. Direct action fuzes – No. 44 fuze – No. 49 fuze 63
60. Time fuze – No. 124 fuze 63
61. Mechanical fuzes 63
62. Hydrostatic fuzes 64
63. Tubes – Percussion tubes – electric tubes 64
64. Primers 64
  Section XIII.- Fireworks.  
65. Deck flares – V.B.S. lights – flares signal distress - Wing tip landing flares 65
  Section XIV.- Magazines and Shell Rooms.  
66. Magazine temperatures and cooling machinery 65
67. Water jacketing of magazines 65
68. Sealing of cordite boxes and cases 65
  Section XV.- Care and Handling of Ammunition.  
69. Protection of B.L. charges 66
70. Venting or cordite cases 66
  Section XVI.- Field and Boat guns.  
71. Field gun equipment of the fleet 66
72. Boat armaments 67
  Section XVII.- Machine Guns and Small Arms  
73. Future Machine Gun Policy – Vickers guns – Lewis guns - Development of .5 in. Vickers machine gun 67
  Section XVIII.- Gas and Smoke  
74. Research work in hand a the Universities and Porton Experimental Station 67
  Section XIX.- Progress in Anti-Aircraft Gunnery.  
75. Control of the main A.A. armament – A.A. guns 68
76. Aldis telescopic ring sight 68
77. Defence against torpedo carrying aircraft 69
78. Defence against Low Flying Aeroplanes 69
79. Targets – Balloons – Gliders – Smoke shell – Controlled aeroplanes – Kites 69
80. Aeroplane detection 69

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Section XX.- Firing Trials with Live Shell. 		 
Article.   Page.
81. Important firing trials with live shell at ship targets. The reports are arranged in the following sections:- XXA, XXB and XXC 69
  Section XXA – H.M.S. “Excellent’s ” Report of Firings against U.B.21, U.141, V.82, and V.44.  
82. General remarks on the trials. 71
83. Detailed results of firing at U.B.21 73
84. Detailed results of firing U.141 75
85. General remarks on trial against T.B.D. V.82 78
86. Detailed results of firing at V.82 79
87. General remarks on trial against ex-German Torpedo Boat Destroyer V.44 81
88. Detailed results of firing at V.44 84
89. Summaries of remarks contained in the reports of the Captain of H.M.S. “ Excellent,” with Admiralty comments, viz.:- Part I. Torpedo Boat V.82. Part II. Torpedo Boat V.44. Part III. Submarine U.B.21 and U.141 90
90. Report of firing trials against V.44 and V.82 – Remarks, re structural damage by Admiralty 97
  Section XXB – H.M.S. “Excellent ” Report on “Nurnberg” Firing.  
91. General remarks on the trial with “ Nurnberg “ 101
92. Detailed results of firing at “ Nurnberg ” 107
93. Summaries of remarks by “ Excellent ” with Admiralty comments on firing trials against “ Nurnberg ” – Conditions for trial (1) Ship heeled to 10 deg. (2) Ship heeled to 20 deg. 121
94. Report of firing trials against “ Nurnberg ” – Remarks, re structural damage, by Admiralty 124
  Section XXC – H.M.S. “Excellent’s ” Report on “ Baden ” Firing.  
95. General remarks on the trials 126
96. Detailed result of each round 131
97. Report of firing trials against “ Baden ” - Remarks, re structural damage, by Admiralty 140
  Section XXI. – Miscellaneous  
98. Heape and Gryll’s Rapid Cinematograph 140
  Section XXII.- Gunnery Publications  
99.   141

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LIST OF PLATES FOR PROGRESS IN GUNNERY MATERIAL, 1921.

_______

  List of Illustrations.  
Fig.   Face Page
1. Additional gear fitted Mark III* Dreyer Tables

9
2. Langley’s Automatic Inclinator 9
3. Henderson’s Director Layer’s Telescope – Mark I 12
4. Henderson’s Director Layer’s Telescope – Mark I 12
5. Henderson’s Director Layer’s Telescope – Mark I 12
6. Henderson’s Director Layer’s Telescope – Mark I 12
7. Diagram of the Principle of Henderson’s Layer’s Telescope 12
7A. Relays in Henderson’s Layer’s Telescope 16
8. Director Control Tower – Main Armament 18
9. Ordnance Q.F. 38 cm. (14.961 in.) 42.4 calibres, German Latest Mark 32
10. “ Lord Clive ” – Premature in 15 in. Mark I Gun 35
11. Trial of 15 in. A.P.C. shell, Mark VA, against K.C. plate 47
12. Photo of Fragmentation of 15 in. A.P.C. filled T.N.T.
" " " " filled shellite. 16.D. Fuze 		52
13. Firing at U.B. 21 – Target diagram 74
14. Firing at U.B. 21 – Target diagram 74
15. U.B. 21 Conning Tower, Rounds I II and III 74
16. U.B. 21 Superstructure, Rounds IV, XII and XIV 74
17. U.B. 21, Rounds V, VI, VII, VIII, XIII, XV and XVI 74
18. U.B. 21, Round XIV – Dent in Pressure Hull 74
19.
U.B. 21, Round XVIII		 75
20. U.B. 21 – General view from firing ship with points of attack marked 75
21.
Firing at U.141 – Target diagrams		 76
22. Firing at U.141 – Target diagrams 76
23. U.141 Conning Tower 76
24. U.141 Conning Tower 76
25. U.141 Conning Tower 76
26. U.141 Port side 76
27.
U.141 Starboard side		 76
28. U.141 Port side 76
29. U.141 Starboard side 76
30. U.141 76
31. U.141 – General view from firing ship with points of attack marked 77
32. Firing at V.82 – Target diagrams 79
33. Firing at V.82 – Target diagrams 79
34.
V.82 – Location of shots No. 7 bursting 4 in. H.E. Fuze No. 18.P.		 80
35. T.B. V.44, Rounds I, II, III, and IV 84
36. T.B. V.44, Rounds V, VI, VII and VIII 86


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  List of Illustrations – continued.  
Fig.   Face Page
37. T.B. V.44, Rounds IX, X and XI 87
38. T.B. V.44, Rounds XII, XIII andf XIV 88
39. V.44 Round XIX – 6 in. H.E. No.18.P. Fuze 88
40.
V.44 Rounds I, III, IV, V and VI 		88
41. V.44 Rounds II, XI, XII and XIV 88
42.
“ Nurnberg, ” Round III – 6 in. H.E. No. 18.P. Fuze (Non-detonating)		 108
  “ Nurnberg, ” Round VIII – 6 in. H.E. No. 18.P. Fuze (Detonating) at gun shield 108
43. “ Nurnberg, ” Rounds IV, IX, XIII, XV, XVI and XVII 108
44.
“ Nurnberg, ” Rounds XVIII, XIX, XX, XXI, XXII and XXIII		 113
45. “ Nurnberg, ” Rounds XXIV, XXV, XXVI, XXVII, XXVIII and XXIX 115
46. “ Nurnberg, ” Rounds XXX, XXXI, XXXII, XXXIII, XXXIV and XXXV 118
47. “ Nurnberg, ” Profile 119
48. “ Baden,” Rounds III and IV 132
49. “ Baden,” Rounds VII and VIII 134
50. “ Baden,” Rounds XI and XII 136
51. “ Baden,” Rounds XVI and XVII 138
52. “ Baden,” Round VIII – A.P.C. 70/30 shellite 16.D. Fuze bursting outside ship 140
  “ Baden,” Round IV – A.P.C. 70/30 shellite 16.D. Fuze bursting inside ship 140
  “ Baden,” Serial No. 14 – A.P.C. 70/30 shellite 16.D. Fuze. Shell entered through 13¾ in. armour at 19 deg. to normal S.V. 1,550 f.s. 140
53. Ex-German Battleship “ Baden ” 140

______________________


9

NOTICE.

This book is not to be considered as authority for demanding stores or altering material or methods.

SECTION 1.

FIRE CONTROL INSTRUMENTS.

1. Dreyer Table Fitted in H.M.S. “ Hood ” – Experience gained during the past twelve months has shown that it is a great improvement on all previous Marks of Dreyer Table. This table is based on a design which is now several years old and may be said to have reached finality on this basis.
In order to meet new requirements a fresh design is required, which is now under preparation at the Admiralty. (G.2401/21.)

Gyro Director Training Gear. – In order to ascertain the best method of carrying out indirect fire from light cruisers, comparative trials will be carried out in light cruisers fitted with Henderson’s Layers’ Telescopes and other light cruisers fitted with gyro director training gear.
The sketch Figure 1 shows the additional gear which is being fitted to the Mark III* Dreyer Tables in “ Delhi.” “Dunedin ” and “ Durban.” This gear is similar to that fitted in “ Hood ” modified to suit Mark III* tables. (G.904/21.)

2. Langley Automatic Inclinator. – This instrument has been fitted for trial in H.M.S. “ Malaya ” instead of “ Queen Elizabeth.”
Figure 2 gives an outline arrangement of the instrument manufactured by Messrs. Elliott Brothers and is placed in the transmitting station. (G.726/21.)

3. Rangefinders.– Trials are being carried out at Fort Cumberland, Eastney, with all types of long base rangefinders, and will include trials with stereoscopic rangefinders and captured German instruments which include a 7.8 metre base stereoscopic instrument which was salved from B turret of “ Hindenburg.” On completion of these trials, the information obtained will be issued to the Fleet.

The first series of trials were carried out with 15 ft. F.X.2, 15 ft. stereoscopic, and 15 ft. F.T.24 rangefinders. Detailed reports have not been received, but the general conclusion is that the coincidence instruments are more accurate than the stereoscopic rangefinder, and the greatest accuracy throughout the trial was obtained from the 15 ft. F.T.24. For light gathering qualities the stereoscopic rangefinder was superior and the F.T.24 inferior to the F.X.2 rangefinder. In this respect the stereoscopic rangefinder operator was able to take ranges for 20 to 30 minutes after the remainder in failing light, but the inaccuracies increased to such an extent that the ranges taken during the last five or ten minutes were of no practical value.

Several instances occurred in which all three rangefinders would give inaccurate results, and their errors, which varied from 50 to 100 yards, increased to 800 or 1,000 yards. The visibility was apparently good, and this error generally occurred when a bright reflection from the sun was thrown on the sea between the rangefinder and the target. (G.11729/21.)

30 ft. Rangefinders.- Trials have been carried out in the Atlantic Fleet with 30 ft. coincidence and stereoscopic rangefinders, but these instruments are handicapped by an unsatisfactory type of mounting. The general conclusions are:-

(1) Under good conditions the 30 ft. rangefinders of either coincidence or stereoscopic type are more accurate than other rangefinders of shorter base length when mounted in similar positions.
(2) The 30 ft. coincidence rangefinders are more accurate :-
(a) When the visibility is good.
(b) When taking “ snap ” ranges.
(c) When taking initial ranges.
(3) The 30 ft. stereoscopic rangefinders are more accurate :-
(d) In poor visibility or failing light.
(e) When affected by vibration.

(G.5615/21.)(C458)

10

30 ft. Rangefinder Mountings. – The design of these mountings has proved unsatisfactory in (a) The method of support ; (b) Elevating gear ; (c) Training gear.

(a) The method of support is insufficient to overcome the vibration when steaming at high speed.
(b) Elevating gear is a type of lever gear, and it has been found that the weight of the 30. ft. instrument is too heavy for the operator. A design of wheel elevating gear has been fitted in “ Repulse ” and “ Queen Elizabeth ” for trial and is satisfactory.
(c) Training gear fitted has too small a leverage and the long base of the instrument causes excessive backlash. This defect has been partly overcome in the mountings as fitted in “ Hood.”
Messrs. Barr and Stroud are preparing a new design which will overcome the above defects and two mountings will be manufactured for trial.
(G.1555/21.)

Rangefinders in Light Cruisers and Torpedo Boat Destroyers.- All rangefinders in Light Cruisers and Torpedo Boat Destroyers suffer from vibration at high speed to such an extent that the results obtained are practically useless.
Trials are being carried out with various types of mountings in ships of the 1st L.C.S., which included an “Argo” mounting which compared unfavourably with the Barr and Stroud type of mountings.
(G.5007/21/)
Comparative trials were carried out with a 3 metre German Stereoscopic Rangefinder and a 9 ft. Barr and Stroud Coincidence Rangefinder mounted in the destroyers “Verity’ and “Whitshed” and the general conclusions arrived at were:-
For initial ranges at ranges of 10,000 and above the coincidence rangefinder is superior.
Under ordinary conditions and steering up to 25 knots there is little to choose between the two types.
At Full Speed the stereoscopic gave the best results, which was partly attributable to the heavier weight of this rangefinder and mounting (especially the mounting), which was 2,144 lb. compared with 1,005 lb.
Interference from funnel gases, the coincidence gave the best results.
Smoke Screen stereoscopic alone could range on the screen. Not much difference in ranging through smoke.
During Firing stereoscopic gave the best results.
Low visibility, stereoscopic gave the best results.
Ranging on a Searchlight. No particular difference.
Ranging on a ship illuminated by searchlight, stereoscopic gave the best results.
Further trials will be carried out from “Winchester” and special attention will be given to obtain the causes and reduction of vibration.
(G.0902/20.)

Bennet type Barr and Stroud Rangefinder Instruction Device.- Five instruments of the above type have been ordered and will be supplied to the following ships for trial:-

One 30 ft. to H.M.S. “Hood.”
One 15 ft. to H.M.S. “Resolution.”
One 15 ft. to H.M.S. “Hawkins.”
One 15 ft. to H.M.S. “Excellent.”
One 15 ft. to H.M.S. “Delhi.”

In arranging the designs for the above ships endeavour has been made so that the cumbersome parts may remain permanently rigged and the amount of erection necessary before use may be reduced to a minimum.
(G.16883/20.)

11

Rangefinder Periscopes.- The present type of trainer’s periscope for 9 ft. mountings in Torpedo Boat Destroyers requires to be lowered every time the rangefinder is covered, and afterwards has to be readjusted each time before use; in addition no movement in elevation is available, and the object rolls out of the field of view, causing unsatisfactory training. Three sets of special brackets so that the periscope can be secured to the body of the rangefinder have been supplied for trial, and this it is hoped will overcome these disadvantages. (G.15370/20.)

Future design of Rangefinders and Mountings.- Experience has shown that the efficiency of any rangefinder depends to a very great extent on the position in the ship in which it is mounted.

Investigations are now being carried out in order to obtain a double mounting, so that two rangefinders may be mounted in director control towers, one of these may be stereoscopic. (G.4725/21.)

______________

SECTION II.

SIGHTS AND SIGHTING.

4. Gun-Sighting Telescopes.- Exhaustive tests and examinations have been carried out at the National Physical Laboratory, Teddington, of various types of German gun-sighting telescopes.

The advantage of the British type is a better definition over the whole of the field. The field of view in the German telescopes is larger, and the definition, except in the centre of the field, is not so goo, being very poor towards the edges.

The great advantage of the German telescopes was the degree of water-tightness obtained. One telescope was salved from a sunken submarine and when opened up the interior was free from moisture.

Messrs. Ottway modified two telescopes which were forwarded to “Excellent” for trial. The following is an extract of the report of the trial carried out with the two modified telescopes :-

Watertightness of G.S. Telescopes.- The two further telescopes mentioned in Messrs. Ottway & Co.’s letter dated 22nd October, 1920, referred to “Excellent” in Admiralty Letter G.16295/20 of 2nd November, 1920, have been received and tested.

2. They are :- one G.S. Telescope, Pattern G.327, and one G.S. Telescope, Pattern G.330.

3. A representative of Messrs. Ottway & Co. was informed of the date of the tests and witnessed them throughout.

4. Trial I.- The telescopes were exposed to steam in a hot bathroom and then subjected to a cold douche. This was carried out twice during a total period of about 30 minutes. Difference of temperature to which the telescopes were exposed is estimated at about 40° F.

5. Trial II.- The telescopes were submerged eyepiece down over the change of focus collar for 4 hours.

6. Trial III.- The telescopes were submerged eyepiece down over the change of power collar for 4 hours.

7. Trial IV.- The telescopes were submerged horizontal in 1 foot of water for 16 hours.

8. After each of these tests the telescopes were carefully examined without opening up, and both the change of focus and change of power collars were worked and found to move freely.

(C458) c2

12

No fogging, penetration of water, or other loss of efficiency could be observed and in view of the severe nature of the tests compared with the probable treatment at sea, it is considered that this design of telescope may be regarded as thoroughly watertight. (G.17747/20.)

In view of these satisfactory results, approval has been given for the above modifications to be carried out to 3-9 V.P. gun-sighting telescopes supplied to Torpedo Boat Destroyers. (G.1995/21.)

Binocular Eyepieces for Gun-sighting Telescopes.- Trials are being carried out in H.M.S. “Excellent” with two designs of binocular eyepiece proposed by Doctor Hanson and Captain Goodyear, with the object of relieving eyestrain and affording protection from blast and flash. (G.2655/21. G.1107/21.)

SECTION III.

DIRECTOR FIRING.

5. Henderson’s Director Layer’s Telescope.- Details of this instrument are shown in plates Figs. 3, 4, 5 and 6, which include the modifications on the original design to allow for application of deflection spotting corrections.

Fig. 3 shows the general optical arrangements including the collimator which produces the illuminated cross wires, and shows the point of aim relatively to the object which is stabilised in the field of view.

Figs. 4 and 5 show the internal arrangements of the appliance, with details of the gyro and its belt connection to the stabilising prism.

Fig. 6 gives an external view showing the means of applying deflection (by means of the collimator) and also the scale for bearing rate.

Fig. 7 shows diagrammatically the principle of the instrument.

Routh outline of principle of Henderson Layer’s Telescopes as used for training (see Fig. 7).

A. Telescope stabilised in space by gyro (B).
Telescope has a black grid in it (C).
F. Spider’s web mounted on gunsight (G) so that it partakes of all movements of the gun and its range and deflection adjustments.
Note.- This grid is really reflected lines from a collimator.
D. A black pointer, mounted in the telescope, which can be moved by hand.
J. The target.
J.K. The line of sight.

The telescope and its grid (C) is stabilised, but the target (J) moves according to rate of change of bearing, and to make telescope and its grid (C) follow it, a method of precessing the gyro at the same speed as the rate of change of bearing is provided, lever (E).

If lever (E) is adjusted to the right rate, then grid (C) always follows the target and on looking through telescope the target appears to remain stationary in the centre of grid whilst the spider’s web (F) moves about as the ship rolls.

The operator is provided with handles (H) by which he can move the gun so as to align the spider’s web (F) on to target and when aligned he presses his trigger and fires.

If the rate of change of bearing has not been correctly gauged the target will move slowly across the stabilised black grid (C), but this does not matter so long as the spider’s web (F) is aligned before the trigger is pressed.

13

To prevent target moving right outside the black grid, the gyro must be pushed round (with another gear not shown) until the target is in the centre of black grid and a new adjustment of lever (D) made to keep it there. Lever (E) will then show the new rate of change of bearing which can be read off on the graduated arc.

Further satisfactory trials have been carried out with this instrument, both in H.M.S. “Valiant” and also in H.M.S. “Dauntless,” including actual firings in indirect fire.

The results of these trials have shown that :-

(a) For Direct Fire.- The instrument is of undoubted assistance to the director layer, and also facilitates picking up the target after brief periods of obstruction to the line of sight from cordite smoke, enemy’s splashes, etc.

A considerable amount of practice is, however, required before the director layer can obtain full value from this instrument.

The director layer has also added to his duties the adjustment of the bearing rate as applied to his telescope, and has to precess the gyro occasionally to keep the object in the centre of his field of view ; this latter operation is only necessary when the bearing rate is wrongly adjusted and when first picking up an object.

These two additional duties correspond to the adjustments of the Henderson Firing Gear as fitted o the trainers’ telescopes in all ships, and are equally simple to operate.

The procedure while in direct fire is as usual, viz. :- The director layer operates the elevation wheel as necessary and fires when his cross wires are on, or if using Henderson’s Firing Gear presses his trigger when his vertical cross wire is on while the trainer keeps on for line.

The great advantage of this telescope is the steadiness of the point of aim, which is not affected by motion of ship.

(b) For Indirect Fire.- The instrument enables single ship indirect fire to be carried out with good accuracy and maintains a very steady point of aim for line in spit of alteration of our ship’s course and speed.

If alteration of enemy’s course and speed are reported by aircraft, the corresponding bearing rate can be applied and hitting should be possible for several salvos depending on the accuracy of the bearing rate applied. If this is only slightly in error the aircraft should be able to spot and correct the error without losing the target.

The procedure whilst in Indirect Fire differs considerable from the normal procedure, viz.:-

The director layer has to perform all duties and his main duty is training and firing (hence ht name “Layer’s Telescope” originally chosen for this appliance is rather unfortunate).

For preference he allows the Henderson Firing Gear to actually make the circuit so that he can devote his whole attention to training and pressing the trigger when his vertical cross wire is on, whilst ensuring that ht elevation will cause the horizontal cross wire to pass the horizon with the roll of the ship.

As the target is invisible he has nothing to do in the way of adjusting the bearing rate on precessing the gyro. In the event of a change of bearing rate being detected, either from aircraft reports or from results of fall of shot, the new bearing rate is calculated by the rate officer and set on the instrument by the phoneman or by an additional operator.

The director trainer is freed from all training and can devote his whole attention to adjustment of the Henderson Firing Gear Telescope and the elevation. If the front horizon is invisible he must have some means of adjusting on the rear horizon, and for this purpose provision has been made in 1921-2 estimates for purchase of a combined “sight inverting attachment and collimator” for use in all ships fitted with means of indirect fire.

Application of spotting corrections for line when in Indirect Fire.- While in direct fire deflection spotting corrections are pot on the deflection dial as usual.

14

When in indirect fire the gun deflections should be kept continually on the sight thereby applying the necessary correction due to any alteration of own ship or reported alteration of enemy. In the event of the enemy becoming visible the director sight is immediately ready for the continuation of direct fire.

Spotting corrections other than the above should not be put on the deflection dial.

Provision is being made in instruments now under manufacture for spotting corrections to be applied to the luminous cross wires in the collimator, provision being made for 5° each way.

Henderson’s Layer’s Telescope Mark II.- A new design of Henderson’s Layer’s Telescope has been designed for trial in H.M.S. “Valiant,” and is now under construction at Greenwich.

The design is generally similar to the Mark I, but the gyro not only stabilises the director line of sight (with provisions for applying bearing rate) but also operates the director training transmitter through a relay be means of differential gear. This is necessary in order to obtain the full value out of the gyro turret training gear when fitted, since with this latter appliance the gyroscopic control automatically eliminates yaw from the turrets, but the displacement control *which causes the turrets to automatically follow the director training pointers) will tend to put it in again, because yaw cannot be eliminated from a hand-trained director. Yaw can, however, be eliminated from the director layer’s line of sight by means of Henderson’s Layer’s Telescope, and if this can also be made to work the director training transmitter, hand worked director sights can then be used in conjunction with the tyro turret training gear without detracting from the efficiency of the latter.

Difficulty has been experienced in the design of Henderson’s Layer’s Telescope Mark II so that it may work in conjunction with Carslake’s Auto Synchronism Transmission Gear ; but it is anticipated that the trial instrument will be completed during 1921.

The following extracts from the report of a Conference held at the Admiralty in April, 1920, deal generally with the subject of the Layer’s Telescope, Henderson’s Gyro Turret Training Gear, and also with Gyro Direction Training Gear.

1. A Conference was held on Tuesday, 27th April, 1920, to consider the Commander-in-Chief, Atlantic Fleet’s letter No. 441/A.H. 835 of the 31st March, 19120, forwarding a report from the Commanding Officer, H.M.S. “Valiant,” on the seagoing trials of Professor Henderson’s Layer’s Telescope, and the remarks thereon by the Vice-Admiral, 2nd Battle Squadron.

2. The conference had under consideration the proposal of the Vice-Admiral, 2nd Battle Squadron, to fit an improved design of Director Sight to Aloft Towers of Capital Ships armed with 15 in. guns, embodying as its primary consideration a form of Henderson’s Layer’s Telescope (modified as proposed in his letter No. 513.D/7 of the 26th March, 1920).

3. The Conference considered the value of the H nderson Laying Telescope under the separate headings of :-

Direct Fire and Indirect Fire.

A. Direct Fire.

4. After examining the report of H.M.S. “Valiant” and its enclosures, it was considered by the Conference that evidence exists that Henderson’s Laying Telescope is of value in direct fire in a heavy ship as –

(i) A help to the layer.
(ii) A bearing rate finder.

And the Conference noted that in these respects it is reported to be superior to the G.D.T. Gear.

Consequently it is recommended that the proposed design of trial director control tower should be adapted to allow such an instrument to be fitted for the sole purpose of finding the bearing rate.

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5. It is necessary, before a decision can be come to as to whether this invention should be fitted in all 15 in. ships, that extended trials should be carried out in a number of heavy ships. For this purpose it is recommended that four additional sets of Henderson’s Laying Telescope with improved precessing arrangements should be constructed and fitted in H.M. Ships “Queen Elizabeth,” “Barham,” “Warspite,” and “:Malaya” in order that more extended trials may be carried out to establish its value and to familiarise officers with the principles involved.

6. It is also recommended that he design of Henderson’s Layer’s Telescope should be developed in the directions proposed by H.M.S. “Valiant,” viz., to enable the gyro to be utilised to eliminate yaw from the director line of sight and spotting corrections to be applied and that Professor Henderson should be asked to make alterations on these lines. This new design of instrument to be fitted in H.M.S. “Valiant” for trial with the Henderson Gyro Turret training system now fitted to one turret and already proposed to be fitted in all turrets of that ship, and also for trial in comparison with the “Valiant’s” power-trained armoured director tower fitted with the Henderson Turret Gyro Training Control.
Note.- It has already been approved to fit the director system of H.M.S. “Valiant” with synchronous transmission to enable the armoured director tower of that ship to be fitted with the Henderson Turret Gyro Training Control, referred to above, and the fact that synchronous transmission is available will permit of the fitting of the proposed new design of Henderson’s Layer’s Telescope to the aloft director tower.
When the above, if approved, has been completed, H.M.S. “Valiant” will be fitted as follows:-

Aloft Director.- Henderson’s modified design of layer’s telescope, with gyroscope providing both “displacement” and “velocity” control of training transmission, i.e., keeping the training transmitter set for both change of bearing and as necessary to eliminate yaw, so that the director layer’s foresight or “spider’s web” should never be off the target for training if the bearing rate is correct.
Note.-See Description of Henderson’s Layer’s Telescope attached.
Turrets.- Henderson’s constrained gyro turret training control and displacement control, training the turrets so as to eliminate yaw and following the director pointers, so that the “turret director trainer” has nothing to do except to set the convergence corrector and possibly get the Slewing pointers into line on larger rapid alterations of bearing.
Armoured Director.- Director sight secured to the armoured director tower and the whole trained by power with Henderson’s constrained gyro turret training control fitted to the tower to provide “velocity” control, i.e. , to relieve the tower trainer of the work of training except for change of bearing and spotting corrections.

This should permit the two systems to be compared, but it is recognised that difficulties will be encountered in the essential work of rendering the armoured tower races and training mechanism respectively true and delicate enough to meet the requirements.

B. Indirect Fire.

7. The Conference consider that it is important that the relative value of various methods of establishing an aiming point for indirect fire should be thoroughly investigated, in order to enable the Admiralty to decide on future lines of progress in this matter.

With regard to this point of view, the President of the Fire Control Table Committee had forwarded to the members of the Conference the following analysis of the “functions required of any complete system of gyro training gear.”

8. Functions required of any Complete system of Gyro Training Gear.
I. Direct Fire.

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Indirect Fire.-

For either direct of indirect fire.

II. Gyro Director Training Gear (Fig. 7A).- This was the first arrangement designed, and owing to war conditions existing gear was made use of.

It is capable of dealing with all the above functions, but a large number of relays have been employed as shown in Sketch I. Each relay detracts from the accuracy of the gear.

The tyro datum line employed (Sperry Compass) is of the “fixed azimuth’ type and is situated below.

Note.- Reports from fleet show that G.D.T. gear as at present fitted is not sufficiently accurate in bad weather, and the backlash due to relays will cause a large proportion of rounds missing for line except under the best conditions.

III. Layer’s Telescope.- The layer’s telescope was originally designed by Professor Henderson to compete with functions (a) and (b), paragraph I.

Only two relays are employed between the Gyros and the guns as shown in Sketch II.

The Gyro is situated aloft and is precessed according to the bearing rate, so that its axis should always be pointing towards the target.

IV. Future System.- (To be used in conjunction with the new Fire Control Table.)

The present intention is to make use of a “fixed azimuth” gyro situated below.

Only two relays need be employed as shown in Sketch III.

V. Improvements to Existing Ships.- The conclusion reached from the result of “Valiant’s” trials is that the layer’s telescope is more accurate than existing gyro director training gear for :-

(a) Measuring the bearing rate.
(b) As an aid to spotter.
(c) For single ship indirect fire (if suitable arrangements can be provided for applying spotting corrections).

The reason why it performs these functions with greater accuracy is because fewer relays are employed.

The gyro has a level control and so has a much slower rate of wander than the sperry against which ti was tested.

Note.- The Henderson modification to the sperry will give the slow rate of wander to the sperry.

VI. Neither the layer’s telescope nor gyro director training gear have as yet been tested for (d) Indirect fire from several ships.

Although single ship indirect fire may be useful for detached ships, the former problem must be solved if indirect fire is to be carried out in a Fleet action.

In view of the great advantages which would accrue to a Fleet whose ships were capable of carrying out simultaneous indirect fire, it is considered that the final solution of this problem should be the ulterior motive of all improvements and trials in existing ships, so long as the efficiency of single ship firing is not impaired.

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VII. The “fixed azimuth” gyro principle (i.e., gyro compass below) is believed to be the most promising method :-

(a) Because there is less difficulty in lining up on the target to start with.
(b) Because a large gyro situated below can be employed, which is likely to be more accurate that a small one aloft.
(Note.- An equal number of relays are required in each case.)
(c) Errors due to bearing rate do not come in.
(Note.- If the layer’s telescope were used for concentrated indirect fire, intercommunication of the bearing rate would be necessary.)

This is one of the principal arguments in favour of adopting the “fixed azimuth” principle for the future design apart from the other advantages of a master gyro system.

VII. Trials in H.M.S. “Rapid.”- Trials of various types of “fixed azimuth” gyros have now been carried out in H.M.S. “Rapid,” from which it appears that a Sperry Compass with Professor Henderson’s modification provides the best available datum line for armament purposes.

It was apparently unaffected by rolling and alterations of course ; the maximum rate of wandering under all conditions did not exceed three minutes of arc per minute of time.

The relative wandering between similar datum lines in several ships (of a Squadron) might be even less.

Four sets of this gear are now on order and are to be fitted to four 15 in. ships.

The arrangements in these four ships would, therefore, be as shown in Sketch IV.

It would be observed that fewer relays are employed by using an Altham Receiver for this purpose than if the necessary dials were fitted to existing gyro director training gear.

This arrangement can only be regarded as a temporary one owing to:-
(1) Complication of the director tower.
(2) Difficulty in applying bearing rates and spotting corrections, but it will provide whatever ships are fitted with the best arrangements at present available for performing the functions required of gyro training gear, and should enable experimental work to proceed on the right lines.

IX.- The principles put forward by the fire Control Table Committee are concurred in by the Conference, and further action is recommended as follows :-

(a) To fit four Altham Receivers in the alfot director towers of the 2nd Battle Squadron ships, in order to provide a datum line for use in employing Henderson’s Layer’s Telescope.
(b) To carry out aiming trials of G.D.T. Gear (Sketch I) in one ship of the 2nd Battle Squadron as soon as the Henderson Controlled Sperry Master Gyro Compasses are fitted.

X.- The system proposed in Sketch III may eventually be fitted in existing ships for trial, but it is desirable to press on with such experiments as can be continued with existing gear in the meantime, and it is not considered that the advantages of any system have yet been proved sufficiently conclusively to justify its installation on a large scale.

6. Gyro Turret Training Gear.- With reference to previous remarks on this gear, little further experience has yet been obtained, but it has been decided to equip all turrets in H.M.S. “Valiant,” and also those in the Capital Ships selected for the trial of the new Main Armament Director Control Tower, which should be completed in 1922.

Owing to delay in manufacture the gear has not yet been installed in “Valiant.” Correction for yaw and alteration of course will also be applied to the director control tower to be built for trial.

7. Local Director Sights.- It has been approved in principle that for all future power worked mountings gun-sights shall be dispensed with and one local director sight for each turret shall be substituted.

(C458) D

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The local director sight will be similar to aloft director sights as regards elevation but will be fixed to the turret for training, having provision only for application of deflection ; thus the trainer at the local director sight will actually train the turret, while the layer’s will operate elevation receivers at the guns.

The sight will be as simple as possible in design and such complications as Henderson Firing Gear and Cross Laying Gear will be omitted. (G.4249/21.)

The advantages of this system over previous ones are :-

(a) Reduction of material provided for alternative methods of fire, one local director sight being provided instead of 4 gun-sights and an open director sight in twin gun turrets, and a proportionally greater saving where triple turrets are adopted.

(b) Better protection to turret and crew in that holes in roof of turret are reduced in number.

(c) Better watertightness.

(d) Saving of personnel in sight setters.

(e) Simplification in training of personnel, as the number of men who have to be taught individual laying will be reduced.

(f) Better facilities for using simultaneous firing of all guns in a turret if required.

(g) The local director sight can be placed close to the officer of the turret, who will be provided with a look-out hood.

The disadvantages are :-

(a) If the local director sight is damaged, means of firing any gun in the turret in local control are lost. This is not likely to occur unless the turret armour is defeated ; the periscope if damaged can be replaced.

(b) Difficulty in finding a suitable position for the local director sight which will be clear of wooding both from guns at all elevations and from ship’s structure. This is not serious, however, and only means the loss of a very few degrees on one extreme bearing.

As these disadvantages only occur when the primary director circuits are damaged they were considered to be of too small importance to outweigh the advantages gained.

Experiments are now being carried out with periscopes in order to obtain a suitable periscope which will look through the side armour in the case of heavy turrets, and which will not suffer from the deficiencies experienced in older pattern gun-sighting periscopes due to loss of light.

There is every reason to suppose that a much improved type of periscope has been designed, and trials are to be carried out.

The use of a periscope with the local director sight has great advantages in reduction of size of holes in armour.

8. The Director Control Tower.- The director control tower is a combination of the director tower and the spotting top and is to be tried in a Capital Ship and H.M.S. “Enterprise.” It is to be embodied in the design of the new capital ships.
(G.0386/21.)

Drawings of the general arrangement for heavy ships are shown on Fig. 8.
(G/01307/20.)

Arrangements for Light Cruisers and 2nd Armament of Capital Ships are generally similar, but in the latter provision is only made for two control officers and the rangefinder is of 12 ft. instead of 15 ft. base, and is mounted out of the centre line.

The advantages to be gained by combining the director tower and the spotting top are :-

(1) All the essential observes are trained together in one tower, thereby avoiding necessity of aids to spotting, etc., giving greater comfort to control officers, and providing greater certainty that director, range-finders, and all control officers are on the same object.

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(2) Owing to the heavy tripod mast being dispensed with, a small amount of weight is saved in spite of the direct control tower being armoured with splinter proof armour ( 2 in. and 1 in.), and the director control tower being mounted on the top of the bridge structure, approximately 100 feet above the water line.

(3) Having all the essential observers in one tower also facilitates the application of gyroscopic inventions for eliminating effect of yaw, so that one instrument will eliminate yaw from the director layer and trainer, the rangefinder, and all the control officers.

The director tower already fitted in H.M.S. “Hood” also carries a 15 ft. range-finder and is trained by power (Williams Janney), and is therefore an intermediate step between the old director tower and the new director control tower. Trials of the power training in “Hoods” tower have so far been very satisfactory, and show that the control of the power training is sufficiently delicate to enable range-taking and director firing to be carried out without independent training of the rangefinder or director sight.

Provision is being made in trial director control towers for independent training of both the director sight and the rangefinder, but if the power training and gyro-scopic control meet expectations, independent training of the rangefinder may be omitted entirely in the future, and possibly also independent training of the director sight, but this latter will depend upon a further series of trials to be carried out on the proposals of the Fire Control Table Committee to apply all deflection including cross levelling in the transmitting room, so that it is never put on the director sight.

9. Carslake’s Auto Synchronous Transmission Gear.- 1. This device is mainly an electrical device, and further details will be found in C.B. 1569, “Annual Report of Torpedo School,” 1919, pages 244 to 246, and in “Vernon’s” Quarterly Letters to the Fleet.

Mention is made, however, in this book owing to the great importance of this invention from the point of view of director receivers.

2. Briefly the arrangement is such that the director training and elevating wheels on the director sights operate one side of hunting switches which control motors situated in the transmitting station. These motors in turn drive the transmitters of the director slewing, training and elevating circuits to the various director towers and turrets, there being separate transmitters for each of these positions. The other side of the hunting switches in the director tower are centred by repeat receivers in this position.

3. What is claimed for this invention is :-

Possibilities of instruments going out of step are reduced, and in particular on changing over from one position to another no lining up is necessary and on putting over the change-over switch all receivers will automatically line up to new controlling position.

In addition to the above, the great advantage from the point of view of director gear is that the limiting speed of transmission can be ignored, and it should be unnecessary in the future to provide clutch gearing between the slewing and the training pointers, since if the slewing handle always drives the training handle slewing receivers will always remain in step, training receivers will get out of step while slewing fast, but will regain step within two seconds of stopping the slewing wheel. The training repeat indicator will show at any time when the speed of slewing is too great for the training repeat to keep in step, and also will indicate when step has been regained.

An incidental advantage of this gear is that each turret and director tower is electrically separate and consequently damage to the circuits in one position will not affect the remainder.

4. Without this device it would be difficult, if not impossible, to utilise several of Sir James Henderson’s inventions, i.e.:-

(a) Application of velocity control to the director tower (to allow for motion of ship in alteration of course and yaw) could not be adopted owing to the certainty of instruments getting out of step if velocity of alteration of course exceeded a certain limit.

(C458) D2

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(b) Similarly, Henderson’s Layer’s Telescope could not be adapted to operate the training and slewing transmitters.

(c) The method of applying cross levelling correction direct to the receiver in turrets would cause instruments to get out of step under extreme conditions of elevation and roll.

(d) Similarly also the practicability of the director control tower will be largely dependent on Carslake Synchronous Gear for the following reason. The D.C.T. trainer merely controls the training engine, and therefore movement of his hand wheel is a measure of rate of training and not of amount of training. Consequently his hand wheel can no longer directly operate the director transmitters, which therefore have to be geared to work off the training rack. This would have introduced great difficulty had it still been necessary to unclutch the training gear before slewing the D.C.T. As explained in paragraph 3 above this, however, will now be unnecessary.
Without auto synchronism it would be necessary to have the director trained by hand entirely independently of the tower as in existing armoured towers.

5. Two sets of this gear will be fitted in H.M.S. “Valiant” and “Revenge” for trial. A further set will be fitted for trial in conjunction with the new director control tower.

7. A recent French invention of Auto synchronous transmission has been brought to the notice of the Admiralty through Messrs. Elliott, who hold the rights of this invention in England. Complete instruments are not at present available for trial, but if this device is favourable it would cover all of the advantages above mentioned in paragraph 4, owing to the high speed of transmission possible ; it would also obviate the necessity of having two motors, one for training and one for slewing, and the receiver could be similar to existing elevation receivers with two pointers geared off one receiver motor.

For the purpose of changing over from one control position to another some form of Carslake’s device would, however, be necessary.

10. Gyroscopes for giving a Vertical Datum Line.- No definite progress has been made in design of gyros to give a horizontal datum line.

Dr. Gray’s Gyro (previously referred to) has been given a trial at sea, but did not meet requirements, being upset by alterations of course and other factors. Sir James Henderson also has a design of gyro for this purpose, but is not at present ready to submit his instrument for official trials.

The difficulties of the problem may be explained briefly as follows. There are two factors to contend with:-

1. Rotation of the Earth.- To maintain the horizontal accurately the gyro must be made to wander in space in order to allow for rotation of the earth and to keep normal to the earth as is shown by attached diagram. This is further complicated by any movement of the ship (or aircraft), i.e., if the ship is steaming east or west.

This compensation can be easily arranged be means of a gravity control, but such a control presents difficulties due to :-

2. Alteration of Course or Speed of the Ship.- This in effect upsets the vertical as far as gravity is concerned, i.e., a plumb line would not remain vertical while ship is altering course or speed, and in order to avoid large errors from this cause the gravity control must be small. Consequently a compromise has to be made.

Dr Gray is still carrying out experiments on his own device, and it is anticipated that further trials will be carried out during the present year with either Sir James Henderson’s Gyro or Dr. Gray’s, or both.

Dr. Gray’s method of dealing with the problem was to temporarily lock the controlling mechanism during alterations of course.

END OF TRANSCRIPTION