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Hedgehog installation on River-class frigate HMS Parret - lso below (Maurice Whiteing) return to Lt-Cdr Mason's researches
or  World War 2, 1939-1945
 by Geoffrey B Mason, Lieutenant Commander, RN (Rtd) (c) 1992

Depth Charges


The only anti-submarine weapon of this type until 1942, it consisted of a simple drum of high explosive which could be set to detonate at varying depths by means of a hydrostatically operated switch. In 1939 small ships were fitted with a trap from which the charges were rolled over the stern and two thrower units which projected the depth charge to a distance of 120ft on either beam. The depth of the submarine was guessed by the Captain as the ASDIC equipment then available had no depth finding capability. Contact by ASDIC was lost when the submarine passed below or behind the ASDIC beam. The ship was conned so that its bow passed over the anticipated future position of the submarine contact. The ASDIC recorder unit incorporated a method of giving a warning of the 'Instant to Fire' for depth charges, which were fired in the sequence:



trap and throwers

trap and

trap again.


This pattern produced a centred diamond formation and allowed for some margin of error.


However wartime experience showed this allowance was insufficient. Later, ships such as the ex-Brazilian 'H' Class had three traps and eight throwers fitted which gave a pattern of 17 charges. Although likely to cover an area at the nominated depth it was necessary to arrange for a variation in the selected depth. One method used was to bolt heavy weights on some depth charges so that they sank more quickly before exploding concurrently with those charges without weights. Modified Mark VII depth charges incorporating additional weight had a sinking speed of 16.5 feet per second which allowed the hydrostatic pistol to be set at depths up to 550 feet. A new explosive, Minol replaced the Amatol originally used. Original design sinking speed was 10 feet per second.


The final pattern selected for use against confirmed submarine targets after many trials and much experience was of 10 charges using two traps (2) and four throwers (2 x 4). In the case of a 'possible' submarine detection a 5 charge pattern was used. Another form of attack used against 'possible' targets considered to be lying stationary was known as a Creeping Attack and as many as 26 depth charges would be used in each instance. (Link Depth Charges)



Depth Charge Mark X - One Ton


This type contained as much explosive as a 10 charge conventional pattern but was fired from a torpedo tube by vessels so fitted. Care had to be exercised in their use since, of necessity, they could not be used against targets near the surface. Because of size and handling considerations only a restricted number of this type were carried depending on number of torpedo tubes. (Mention HMS Beverley)





This was the first Ahead Throwing Weapon (ATW), which replaced the "A" gun mounting in some ships or in some escorts was fitted on the foc'sle. It produced an elliptical pattern of 24 charges at submarine targets in firm contact ahead of the ship. This weapon had the disadvantage of requiring a 'hit' before it could detonate. As a result it had no demoralising effect and was not well supported by documentation which caused maintenance and installation problems. (Link The Hedgehog)


HMS Parret (click for enlargement)



Squid Mortar


First used operationally in 1944 the Squid weapon was a three barrelled mortar with a range of about 300 yards. Its mounting was stabilised to take account of roll and yaw. Each projectile contained about 200lb of a new explosive Minol II with a sinking speed about twice that of the Hedgehog. Ships with one mounting produced a triangular pattern with 120 foot sides and those with two mountings an additional pattern at a lower depth - hopefully with the target submarine between the two layers.


It was the first A/S weapon which was provided automatically with target depth information from an ASDIC set specially designed for this purpose. The depth information was used to set the mortar bomb detonator so that it would explode at the required depth of the target.


The Squid had a very impressive success rate compared with conventional depth charge and Hedgehog attacks. (Link Squid (Weapon))



Notes on Depth Charges based on Warship Profile No. 20 by Captain P. Dickens, RN (Rtd).

"Seek and Strike" by Willem Hackmann


return to Lt-Cdr Mason's researches
or  World War 2, 1939-1945

revised  5/12/10