21-in Mark IV Torpedo (UK)

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The 21-in R.N.T.F. Mark IV Torpedo was a British torpedo developed at the Royal Navy Torpedo Factory in 1915.[1]

Development and History

Fractures of 21-in Mark II*** Torpedoes in firings from Calliope at 29 knots indicated a need for a strengthened torpedo.[2] The first torpedoes tested tended to break surface on the range at Long Loch.

Mark IV

It differed from the Mark II*** in ten particulars, including a generally stronger form, tail fittings similar to G.S. 1 as fitted in the 18-in Marks VIII and VIII*, a tappet engine and injection oil which it was hoped might deliver 12,500 yards range. In its initial runnings at Loch Long, it caused great trouble by breaking surface.[3]

On vital feature of this new torpedo was that it had a three-speed rather than two-speed generator, which permitted them to each have an Extreme Range (E.R.) setting that could be conveniently chosen (formerly, E.R. torpedoes were hard-plumbed to deliver this performance).[4]

By 1916, it was being described in more operational terms. The weapons were R.N.T.F. only and had two warheads, the IVA of 400 pounds T.N.T. extended the length 2.3 inches beyond that of the Mark II type, and the IVB of 500 pounds T.N.T. which was fully 9.8 inches longer than the Mark II warhead.

  • 44.5 knots to 4,500 yards (High Speed)
  • 25 knots to 15,000 yards (Medium Speed)
  • 21 knots to 18,000 yards (E.R.)

In 1917, it was decided that depth-taking was so unreliable at High Speed settings, with 70 foot dives not being unusual that all IV and IV* torpedoes should be reset to 35 knots and 6,000 yards until such time as XX Depth Gear became available.[5]

In May, 1918, some of the torpedoes now had a 35 knot High Speed setting in place of the 44.5 knot speed, giving 6,000 yards range at 2650 psi.[6]

The 2650 psi pressure was the "action" pressure; normal working pressure was 2500. Ranges were 300 yards less at 44.5 knots and 1,000 yards less at lower speeds at the normal pressure. A 2000 psi charge gave reduced the 44.5 knot setting to 3,000 yards at 43.75 knots.

In December, 1918, the 44.5 knot range was increased to 4,550 yards, but performance and settings were otherwise unchanged.[7]

Mark IV*

Introduced in 1917, these torpedoes had four settings and included Sandford's Gyro Control Gear.[8]

In submarine use (at least), in 1917 it was decided that they were to deliver:[9]

  • 45 knots to 4,500 yards
  • 29 knots to 11,000 yards
  • 25 knots to 15,000 yards
  • 21 knots to 18,000 yards

In other use, the 45 knot speed became 44.5 knots. The torpedoes were in both H.B. and S.L. pattern. It was noted that the torpedoes ran 1 to 1.5 knots faster for the first 3⁄4 of the range.[10]

In 1917, it was decided that depth-taking was so unreliable at High Speed settings, with 70 foot dives not being unusual that all IV and IV* torpedoes should be reset to 35 knots and 6,000 yards until such time as XX Depth Gear became available.[11]

In May, 1918, the torpedo was noted as having the following settings at a charge of 2650 pounds per square inch, though each torpedo would have either the 35 or 44.5 knot setting, but not both:[12]

  • 44.5 knots to 4,500 yards (High Speed)
  • 35 knots to 6,000 yards (High Speed)
  • 29 knots to 11,000 yards (Medium Speed)
  • 25 knots to 15,000 yards (Medium Speed)
  • 21 knots to 18,000 yards (E.R.)

The 2650 psi pressure was the "action" pressure; normal was 2500. Ranges were 300 yards less at 44.5 knots and 1,000 yards less at lower speeds at the normal pressure.

In December, 1918, the performance and settings were unchanged.[13]

Footnotes

  1. ↑ Annual Report of the Torpedo School, 1915. p. vii.
  2. ↑ Annual Report of the Torpedo School, 1915. p. 37.
  3. ↑ Annual Report of the Torpedo School, 1915. p. 37.
  4. ↑ Annual Report of the Torpedo School, 1916. p. 44.
  5. ↑ Annual Report of the Torpedo School, 1917. p. 26.
  6. ↑ Grand Fleet Gunnery and Torpedo Orders. p. 16.
  7. ↑ Grand Fleet Gunnery and Torpedo Orders. p. 16.
  8. ↑ Annual Report of the Torpedo School, 1917. p. 19.
  9. ↑ Annual Report of the Torpedo School, 1917. pp 25-26.
  10. ↑ Annual Report of the Torpedo School, 1917. p. 28.
  11. ↑ Annual Report of the Torpedo School, 1917. p. 26.
  12. ↑ Grand Fleet Gunnery and Torpedo Orders. p. 16.
  13. ↑ Grand Fleet Gunnery and Torpedo Orders. p. 16.

Bibliography

See Also

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