Torpedo Deflection Sight Mark IV

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Telescope model [1]
Telescope model [2]

The Torpedo Deflection Sight Mark IV Types were a family of British torpedo deflection sights created for use from armoured sighting positions in capital ships armed with 21-inch torpedoes.[3] As initially delivered, they were telescopic. Later, they were modified into a periscopic design.

They were manufactured by Vickers.[4][5]

Design

These sights initially featured a telescope sitting atop the mechanism, able to pitch up and down by 10 degrees, these would be sited in port/starboard pairs in armoured control positions, peeking out the slot in the armour. It also had open sights.[6][7]

The bottom-most cylinder was fixed and showed the relative bearing. The next scale was also fixed and depicted the Gyro Angle. The top scale moved with the telescope carrier and showed deflection. It could be fixed in one of several positions corresponding to different torpedo settings. A pointer moving with the telescope carrier, but able to be revolved relative to it by gearing indicated against all these scales.

The deflection would be set to zero and the telescope trained onto the target. The pointers would then indicate the required gyro angle for the zero deflection case. The deflection would then be dialed in by use of a milled head until it read the proper value. This moved the gyro angle reading by an amount equal to the director angle.

These were made in port and starboard "handed" models owing to the various angles of tube inclination between ships and these angles being reversed on the two broadsides. A suffix of "a" was used for starboard, and "b" for port.

  • Mark IVa and IVb were 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 the reader.

Allocation

The first four, with telescopes, were delivered in February 1917 and issued to Warspite for trial. The results were highly satisfactory and justified the decision to adopt them for heavy gun ships.[8]

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.

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.[9]

Alterations

Periscope of T.D.S. Mark IV[10]
Notice open sights alongside.
T.D.S. Mark IV*[11]
Depicted with the Loose Gyro Bearing Ring fitted.
T.D.S. Mark IV*[12]
Also with Loose Gyro Bearing Ring.

Following the trial in Warspite, concerns of blast and a desire to drive the Torpedo Control Evershed (see ARTS 1917 page 208) from the sight prompted interest in moving from the telescope to periscope binoculars.[13]

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. [14]

Loose Gyro Bearing Ring

Loose Gyro Bearing Ring[15]

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.[16]

The rings would be used as follows.[17]

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

See Also

Footnotes

  1. ↑ Handbook of Torpedo Control, 1916, Plate 9.
  2. ↑ Handbook of Torpedo Control, 1916, Plate 10.
  3. ↑ Annual Report of the Torpedo School, 1917, p. 190. (C.M.O. 3977 of 1917, G. 14352/17)
  4. ↑ Handbook of Torpedo Control, 1916, p. 24, Plates 9, 10.
  5. ↑ N.B.: There is some small level of uncertainty that the telescope sight shown in Handbook of Torpedo Control, 1916 is a Mark IV. I find the similarity of the base compelling, alongside the knowledge that the sight did start as a telescopic instrument and then advanced to a periscope model. The T.D.S. Mark VII is just too different from the unnamed telescopic model in the Handbook.
  6. ↑ Handbook of Torpedo Control, 1916, p. 24, Plates 9, 10.
  7. ↑ Handbook of Torpedo Control, 1917, p. 190.
  8. ↑ Annual Report of the Torpedo School, 1917, p. 190.
  9. ↑ Annual Report of the Torpedo School, 1918, pp. 157-158.
  10. ↑ Annual Report of the Torpedo School, 1918, Plate 110.
  11. ↑ Annual Report of the Torpedo School, 1918, Plate 112.
  12. ↑ Annual Report of the Torpedo School, 1918, Plate 113.
  13. ↑ Annual Report of the Torpedo School, 1917, p. 190.
  14. ↑ Annual Report of the Torpedo School, 1918, pp. 157-158.
  15. ↑ Annual Report of the Torpedo School, 1918, Plate 111.
  16. ↑ Annual Report of the Torpedo School, 1918, p. 158
  17. ↑ Annual Report of the Torpedo School, 1918, pp. 158-159.

Bibliography

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