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
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
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 Charge Mark X - One
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 –
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)
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 –
Notes on Depth Charges based on Warship
Profile No. 20 by Captain P. Dickens, RN (Rtd).
"Seek and Strike" by Willem Hackmann