Torpedo Deflection Sight

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As the war developed, the Royal Navy was not happy with its Torpedo Directors, which combined calculating functions based on the director triangle with the sighting function. It devised a family of Torpedo Deflection Sights of several Marks which sought to encompass only the simple task of sighting, leaving the task of calculating the director angle to external means.

Geometric Model

The deflection sights worked on the deflection triangle — that formed by the line-of-sight, the path of torpedo, and the line perpendicular to line-of-sight that passes through the point of impact. That last line is the Torpedo Deflection, or speed-across attributable to enemy motion.

The charm seen in such a geometric model is that for any given speed of torpedo, a single radial scale can be etched that converts torpedo deflection to the suitable director angle. This means a director's proper setting can be communicated quickly and according to a measure (enemy speed-across) that might be roughly guessed with some accuracy in an emergency.

Mark I

This was the name given to all A.W. directors converted to being deflection sight, and by the end of August, 1918, had been or was being fitted to tubes in all light cruisers "Attentive" and after and TBDs "E" class and after armed with RGF and RNTF heaters. Due to limited numbers of Mark I, some later ships are getting TDS Mark III

Designed before introduction of medium speed setting (ARTS 1916, p 45), and so the deflection rings are for the 3 speeds of one Mark of torpedo. When getting medium-speed-capable torps, these would require adaptation.[1]

Large Deflection Rings for T.D.S. Mark I [2]
The distinguishing letters would be circled. Subscripts denote the reverse side of another ring.
Distinguishing Letter Graduated Speeds (knots) for Torpedo Marks
S 25, 29, 35 21-in Marks IV* and V with 35-knot setting
S1 25, 29, 44.5
L 21, 25, 35 21-in Mark IV with 35-knot setting
L1 21, 25, 44.5
K 21, 25, 44.5 21-in Mark IV
K1 19, 24, 44.5 21-in Mark II*****
Q 19, 24, 35 21-in Mark II***** with 35 knot setting
Q1 18, 23, 35 21-in Mark II-II**** E.R. 3 with 35-knot setting
M 19, 24, 44.5 21-in Mark II*****
M1 18, 22, 44.5[3] 21-in Mark II-II**** E.R. 3
P 18, 23, 44.5 21-in Mark II-II**** E.R. 3
R 18, 23, 44.5 21-in Mark II-II**** E.R. 3
R1 18, 29, 45 21-in Mark I-I*
T 19, 29, 41 18-in Mark VII-VII*****
T1 19, 29, 35

By mid 1919, delivery of all the rings was still being completed.


Mark II

(main article)

These were converted line of sight directors. By August, 1918, they had been issued to TBDs for use on the bridge, except in "V" class and later which have Mark III in this position.

Mark III

Modified Rings for T.D.S. Mark III[4]
Handles added to alter setting shown in blue.
Modification for T.D.S. Mark III[5]
Modification to allow amount of course alteration required to bring sights on.

This was to be the universal sight for LCs (S.F. or A.W.) and TBDs for control positions or on tubes. By (T.O. 232/17), they wre approved to be issued as follows:[6]

  • four to each LC with 23-in (H.B. or S.L.) for use on fore RF or compass platform and after control positions.
  • Two to Flotilla Leaders and to TBDs "V" class and later for use on bridge
  • for use on A.W. training tubes when the supply of earlier types is exhausted.

By July 1919, supply was in this state:

  • Four to each Light Cruiser armed with 21-in H.B or S.L. torpedoes, to be fitted to fore bridge and after control positions (issuance complete)
  • Eight to each of Light Cruisers Danae class and later (being completed with these supplied)
  • Four to each Raleigh class Light Cruiser
  • Four to some "V" class destroyers for use on the fore bridge. (Supplied on completion)
  • Two to existing Flotilla Leaders for use on the fore bridge. (Supply in process)
  • Two to nine of the "V" class destroyers for use on the fore bridge. (Supplied on completion)
  • Four to FLs of Scott class and later. (Supply in process)
  • Four to "W" class destroyers and later ("W" and "S" were supplied on completion)
  • One for each Torpedo Attack Table in Destroyer Depots (Supply in process)

Issues with the deflection rings becoming stiff from salt water prompted a modification to add 3 lugs to help move the ring as needed. New sights would be completed with these in place, and the staff of light cruisers were to adapt their existing sights with destroyers having the work performed by their depot. Similar issues were seen in the need to permit torpedo officers to tell their captain how much more of a turn would be required before the torpedo could be fired, and the work was executed in the same manner.[7]

Mark IV Types

Periscope of T.D.S. Mark IV[8]
Notice open sights alongside, which would not afford the user the blast protection.
T.D.S. Mark IV*[9]
Depicted here with the Loose Gyro Bearing Ring fitted.
T.D.S. Mark IV*[10]
Depicted here with the Loose Gyro Bearing Ring fitted.

Being supplied to BBs and BCs with 21-in torpedoes for use in armoured control positions (C.M.O. 3977 of 1917, G. 14352/17)[11] These were made in port and starboard 'handed' sides, and for various angles of tube inclination. "a" for starboard, "b" for port.

  • Mark IVa and IVn for ships with tubes at 90 degrees (Hood, Repulse, Courageous, Royal Sovereign, Colossus and Lion classes, and Furious and Orion
  • IV*a and IV*b for ships with forward tubes at 80 degs and aft at 100 degs: Queen Elizabeth and Iron Duke classes
  • IV**a and IV**b for ships with tubes at 80 degs: King George V class and Orion class except Orion
  • IVa (special) and IVb (special) for ships with tubes at other assorted inclinations: Tiger, Canada, Agincourt, and Erin

The differences between the sights was limited to the gyro angle scale and reader. The first four were delivered in Feb 1917 to Warspite for trial. Report was highly satisfactory and justified the decision to adopt them for heavy gun ships. Concerns of blast and the desire to drive the TC Evershed (see ARTS 1917 page 208) from the sight prompted interest in moving from telescope to periscope binos.


These sights were to be provided two per ship by C.I.O 3977 of 1917, and by the end of 1918, all ships had been so fitted.[12]

Unfortunately, the proposal to add binocular periscopes to better shield the user from gun blast was found unworkable for the added weight (50 pounds!) and a lighter design did not seem easily achievable given other commitments. As a result, a monocular periscope of field 13 degrees and power 3 was chosen that could be elevated or depressed 12.5 degrees. The periscope was to be kept in its storage box when not in use. A set of coloured shades for the eyepiece were provided.

The periscope proved satisfactory to the degree that it was proposed that the Evershed torpedo control transmitter should be placed here rather than on the torpedo rangefinder.

By mid 1919, Royal Sovereign, Benbow, Iron Duke Lion Emperor of India 'Marlborough, Ramillies and Queen Elizabeth were completely equipped and Renown had two. Other existing T.D.S. Mark IVs were to be adapted for the periscope at the next refit.[13]

Loose Gyro Bearing Ring

Loose Gyro Bearing Ring[14]

To assist in divisional torpedo control, a ring was added so a gyro compass bearing from 0 to 360 degrees could quickly be converted to a gyro angle. Some sights (IV, IV**, and IV Special for Agincourt and Erin) could be adapted by merely adding pointers to the deflection readers, whereas others needed a completely new reader (IV* and IV Special for Canada and Tiger). These would be added by Portsmouth Yard when sights were updated to the periscope, but the staff of the ships listed above would adapt their fully updated sights themselves.[15]

The rings would be used as follows.[16]

When told to fire a torpedo on a given gyro bearing, the user would

  1. turn the loose ring to the bearing of ship's head, placing it at zero degrees on the bearing scale on the after side of the instrument.
  2. turn the reader by using the deflection working head until the new extension pointer is over the given gyro bearing
  3. the tube arrows would then indicate the necessary gyro angle

When told to fire a torpedo at a target on a given gyro bearing, the user would

  1. turn the loose ring to the bearing of ship's head, placing it at zero degrees on the bearing scale on the after side of the instrument.
  2. Set deflection to zero
  3. turn the sight by using the training head until the pointer is over the given gyro bearing
  4. apply the desired deflection
  5. the tube arrows would then indicate the necessary gyro angle

Mark V

T.D.S. Mark V[17]

The Mark V had just a single deflection ring, bearing the letter designation of a C in a circle, etched for the 26.75-27.25 knot setting of the 18-in Mark IV and the 14-in R.G.F. Mark X*.

By mid 1919, the 14-in torpedo tubes had been removed from the P Boat Class (1915), and so the T.D.S. Mark V was removed from them, leaving them only on the subset of the "S" class destroyers that carried 18-in tubes. Shortly thereafter, those ships would also lose their 18-in torpedos, leaving no vessels carrying the Mark V.[18]

Mark VI

T.D.S. Mark VI[19]
Hinged Sight for Special Service Vessels[20]
It is not clear whether this device is related to the Mark VI.

Designed by Defiance, this was to be an emergency sight for fixed above-water tubes on capital ships, but apparently not to be fitted on the tubes themselves. By mid-1919, however, no approval had been given to manufacture the sights. The sight could hinged down, and was suitable for use out a narrow opening, as its foresight was on the pivot.

Details on its use and design are provided in the Annual Report of the Torpedo School, 1918.[21]

Mark VII

(main article)

These periscopic sights could look out through the horizontal view slot of an armoured space on a battleship or battlecruiser and thus permit the operator to avoid gun blast.

Mark VIII

In mid-1919, this sight was still in the design stage. It was intended for principal control officers in capital ships. At its core, it would be similar to a T.D.S. Mark III, but with two clear arc indicators to show the arcs of 70 degrees to 110 degrees from friendly capital ships. A gyro ring worked by a milled head would permit fire to be ordered on any gyro bearing within the clear arc limits.[22]

See Also

Footnotes

  1. ↑ Annual Report of the Torpedo School, 1917, p. 190.
  2. ↑ Annual Report of the Torpedo School, 1918, p. 155.
  3. ↑ Discrepancy between Mark I and Mark II
  4. ↑ Annual Report of the Torpedo School, 1918, Plate 109.
  5. ↑ Annual Report of the Torpedo School, 1918, Plate 108.
  6. ↑ Annual Report of the Torpedo School, 1917, p. 190.
  7. ↑ Annual Report of the Torpedo School, 1918, p. 157.
  8. ↑ Annual Report of the Torpedo School, 1918, Plate 110.
  9. ↑ Annual Report of the Torpedo School, 1918, Plate 112.
  10. ↑ Annual Report of the Torpedo School, 1918, Plate 113.
  11. ↑ Annual Report of the Torpedo School, 1917, p. 190.
  12. ↑ Annual Report of the Torpedo School, 1918, p. 157.
  13. ↑ Annual Report of the Torpedo School, 1918, pp. 157-158.
  14. ↑ Annual Report of the Torpedo School, 1918, Plate 111.
  15. ↑ Annual Report of the Torpedo School, 1918, p. 158
  16. ↑ Annual Report of the Torpedo School, 1918, pp. 158-159.
  17. ↑ Annual Report of the Torpedo School, 1917, Plate 53.
  18. ↑ Annual Report of the Torpedo School, 1918, p. 159.
  19. ↑ Annual Report of the Torpedo School, 1918, Plate 114.
  20. ↑ Annual Report of the Torpedo School, 1917, Plate 54.
  21. ↑ Annual Report of the Torpedo School, 1918, p. 159.
  22. ↑ Annual Report of the Torpedo School, 1918, p. 160.

Bibliography

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