Category:Depth Charge (UK)

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The British used a variety of depth charges in the war.

The first cross-section report on the types in use is found in the Annual Report of the Torpedo School, 1915.[1]

Conception

The primary characteristic of these were that they were to explode at a given depth. The firing means (for all but the Egerton depth charge) was either mechanically when a float pulled a cable of a given length taut, or hydrostatically when pressure forced a diagram to compress a spring.

Some of the devices were adapted from other weapons. All were developed in Vernon except the Egerton depth charge and the anti-submarine grenade.

It was envisioned that opportunities for use would be rare, and so it was desired that they be kept ready "for instant use."

Type A

Total weight 210 pounds. 32.5 pounds of gun cotton initiated by a primer of 2.25 pounds. Set to be triggered mechanically by a float and wire system at a depth of 40 feet. It had a 10 foot danger radius. Adapted from the "Vernon boom", it was the first type to be used and was in general use by small craft in October 1915.

Type B

A modification of the Type A, it could be set for either 40 or 80 feet in depth, and the overall weight had been reduced to 170 pounds without altering the explosive weight. It was also in general use by small craft in October 1915.

Type C & C*

Adapted from Aeroplane bomb R.L. Pattern 22262, it was streamlined like a small bomb and had 25 pounds of T.N.T. or Amatol initiated by 0.75 pounds of Tetryl. It had a 10 foot danger radius.

The Type C was triggered by a float at either 40 or 80 feet, and the Type C* was hydrostatically triggered at 50 feet. It sank at 10 feet per second. It was about to be issued to small craft in October 1915, and by December the C was being issued and the C* was soon to be ordered.

Type D & D*

This was a much larger weapon, the D* being, apparently, a smaller charge within the Type D shell. The Type D/D* weapons had 300/120 pounds of T.N.T. or Amatol initiated by 2.25 pounds of gun cotton, yielding total weights of 430/250 pounds and danger radii of 70/35 feet.

Hydrostatic triggering was for 40 or 80 feet and the rate of sinking sadly illegible in my photographed source, but seemingly different for the two types. The sketch of the two seems to show that the Type D had a parachute assembly to slow its rate of sinking. Given its considerable danger radius, the Type D's 40 foot setting was never be used when the depth of water would permit the 80 foot depth to be used.

A special primary safety gear, in series with the main trigger, prevented initiation in water shallower than 10 feet.

The weapon was of a wholly new design for the purpose and apparently the familiar cylindrical shape. It was envisioned that these would become the standard large and small charges.

On December 1, 1915, the Type D was about to be issued and the Type D* was under trial.

Type E

This was similar to Types A and B, in that it was adapted from the Vernon boom, but the non-explosive weight had been drastically reduced, allowing for a much more powerful explosive punch in the same overall weight.

A cylindrical charge with a charge of 100 pounds T.N.T. or Amatol and 16.25 pounds guncotton, it was initiated by 2.25 pounds of gun cotton, yielding a danger radius of 35 feet. It had an overall weight of 220 pounds and sank at 5 feet per second before being triggered by a float and wire at 40 or 80 feet.

By the 1st October 1915, it was to be issued to motor launches, whalers, sloops and patrol craft. It was actively being issued by 1 December.

It was hoped that in most cases, remote dropping of these from the bridge position would help in their precise placement.

Type F

A club-like charge suitable for use by bomb-throwers (guns worked by compressed CO2), a 1 pound initiator of Tetryl set off 70 pounds of T.N.T. at 50 feet by a hydrostatic trigger. The danger radius was 25 feet. It was under trial in October 1915, and these were nearly completion by early December. The guns, firing on a fixed elevation on a turntable and trained by a hand spike, could throw the bomb up to 500 yards horizontally. Lower ranges were achieved by lower firing pressures, read off a gauge.

A special primary safety gear, in series with the main trigger, prevented initiation in water shallower than 10 feet.

Egerton

Adapted from a modified sweep, Egerton charges were in equal pairs, separated by 120 feet of electrical triggering wire. Each of the two charges was 75 pounds of T.N.T. set off by 2.25 pounds gun cotton primer. Each had a 25 foot danger radius and the total weight of the assembly was 200 pounds. These were in general use by destroyers and other vessels in early October 1915, but were to be replaced in use by the Type D as supplied increased.

Cruiser Mine

Adapted from a spherical service mine, 250 pounds of gun cotton were initiated by 2.25 pounds G.C. primer, producing a danger radius of 52 feet. A hydrostatic trigger set it off at 45 feet. The overall weight was 1150 pounds, giving it a sink rate of 7-8 feet per second. It was in general use by early October 1915.

Anti-Submarine Grenade

A design from the French Navy, it was in general use in the Mediterranean in early October 1915. 35 pounds of G.C. with 18 ounces G.C. primer were set off hydrostatically at 33 feet. It sank at 3.5 feet per second. The danger radius was probably similar to the Type A-C's, based on charge weight: 10 feet.

Footnotes

  1. Annual Report of the Torpedo School, 1915. pp. 164-5, Plate 73.