British ASW Weapons

British
ASW Weapons
Updated 05 September 2006

ASW Information .

General Notes

Dropping depth charges off the stern via a rack or track was standard practice for destroyers and destroyer escorts in both World Wars. Ahead firing weapons saw service introduction in 1917 and again in late 1942, but were relatively unsuccessful in the Royal Navy until 1944. Modern day ASW weapons are mainly torpedoes and are listed in the Torpedo section of Naval Weapons.

Effectiveness

In mid-1916 the D-type depth-charge had been developed, but there were reliability problems with the firing pistols. Production of these much needed weapons was hampered by technical difficulties, resulting in strict rationing of their use by 1917. Usually, escorts carried no more than 35 DC, which, given the unreliable detection methods of the time, was considered to be quite inadequate. The Allies sank about 30 German submarines with DC in World War I; two in 1916, six in 1917 and twenty-two in 1918.

In 1939 the only British ASW weapon for surface ships was still the depth charge and there was no satisfactory aircraft borne weapon. The depth charge remained the main British ASW weapon until the middle of 1944 when Hedgehog and Squid started sinking more U-Boats.

Postwar, the ASW torpedo has been the primary anti-submarine weapon, although the Limbo mortar developed just after the end of the war was used throughout the 1980s on Canadian and other Commonwealth vessels.

Other Information

Most early sonar systems lost the target submarine on close approach. "Blind Time" is the time between when sonar lost the target and the time when a weapon could be launched. Usually, the attacking ship would "sprint" to reduce blind time. For depth charges, this meant that they were dropped or fired after the sonar contact was lost. Hedgehog was the first "ahead-fired" weapon that could be used while the attacking ship still had sonar contact on the target submarine.

British ASW during World War II .

The following table shows British success against German U-Boats during World War II. A "half" represents a shared kill.
Period	Surface Ships		Shore-based Aircraft		Shipborne Aircraft		Bombing Raids
1939 - 1942	72		31.5		3		---
1943 - 1945	153		177		16.5		22
Total	225		208.5		19.5		22
The following table shows the relative effectiveness of British surface ships against U-Boats using Depth Charges, Hedgehog and Squid. A "half" represents a shared kill.
Period	Depth Charges		Hedgehog		Double Squid		Single Squid
	Attacks	Kills	Attacks	Kills	Attacks	Kills	Attacks	Kills
Jan - June 1943	554	27.5	53	4.5	---	---	---	---
July - Dec 1943	4,011	15	49	4	---	---	---	---
Jan - June 1944	404	30	70	10	---	---	3	0
July - Dec 1944	98	5.5	37	13	6	2.5	17	0
Jan - May 1945	107	7.5	59	15.5	21	8.5	3	2
Total	5,174	85.5	268	47	27	11	23	2

Depth Charges . Types A and B .

Date Of Design	1914
Date In Service	1915
Total Weight	N/A
Explosive Charge	32.5 lbs. (14.7 kg) gun-cotton
Sink Rate / Terminal Velocity	N/A
Settings	N/A
Notes: Float and lanyard type. Introduced into service in January 1915 to the Auxiliary Patrol in limited numbers. Needed to be within 20 feet (6 m) of a U-boat in order to be effective. No U-boat was damaged or sunk by these and they were rarely used.

Types C and C* .

Date Of Design	1914
Date In Service	1915
Total Weight	N/A
Explosive Charge	Either 35 lbs. (15.9 kg) or 65 lbs. (29.5 kg) gun-cotton
Sink Rate / Terminal Velocity	N/A
Settings	Type C: 40 or 80 feet (12 or 24 m) Type C*: 50 feet (15 m)
Notes: Aircraft Depth Charge where the size of the charge was determined by how much weight the aircraft could carry. Type C was float and lanyard type while Type C* used a hydrostatic pistol. No U-boat was damaged or sunk by these and they were rarely used.

Type D .

Date Of Design	1915
Date In Service	1916
Total Weight	About 420 lbs. (191 kg)
Explosive Charge	300 lbs. (136 kg) TNT
Sink Rate / Terminal Velocity	7 fps (2.1 mps)
Settings	40 or 80 feet (12 or 24 m)
Notes: The first British depth charge that used a hydrostatic pistol. Issued to the fleet starting in January 1916. The British estimated that this would destroy a U-boat at 70 feet (21 m) and would cause severe damage out to 140 feet (42 m). The real numbers were probably much smaller than these figures. Production problems meant that most ships initially received no more than two DCs and even by the end of 1916 the standard outfit was four DCs. The supply remained limited until June 1917. There is conflicting evidence as to which U-boat was the first sunk by these depth charges, with the probability being that it was UB-29 on 13 December 1916 by HMS Landrail. The USN agreed in 1917 to produce 15,000 of the Type D for the Royal Navy, although it was considered to be inferior to their own Mark II, as the Type D had a tendency to explode prematurely when used with a projector.

Type D* .

Date Of Design	1915
Date In Service	1916
Total Weight	About 240 lbs. (191 kg)
Explosive Charge	120 lbs. (54 kg) TNT
Sink Rate / Terminal Velocity	about 6 fps (1.8 mps)
Settings	40 or 80 feet (12 or 24 m)
Notes: This was issued to slow-moving ships as it was felt that the larger charge of the Type D would probably blow off the ship's stern.

Type D Mark III .

Date Of Design	1916
Date In Service	1917
Total Weight	About 420 lbs. (191 kg)
Explosive Charge	300 lbs. (136 kg) TNT (replaced with Amatol about 1917)
Sink Rate / Terminal Velocity	7 fps (2.1 mps)
Settings	300 feet (91 m) max
Notes: The standard DC of the latter half of World War I and still in service in 1940. Estimated in World War II that the effective kill radius was 14 feet (4.3 m). This DC copied the USN Mark II design of using an external dial that could be easily set before dropping.

Type E .

Date Of Design	1914
Date In Service	1915
Total Weight	N/A
Explosive Charge	100 lbs. (45.4 kg) gun-cotton
Sink Rate / Terminal Velocity	N/A
Settings	N/A
Notes: Float and lanyard type. Introduced into service in January 1915 to the Auxiliary Patrol in limited numbers. Needed to be within 70 feet (21 m) of a U-boat to be effective. No U-boat was damaged or sunk by these and they were rarely used.

Mark VII .

Date Of Design	N/A
Date In Service	1939 (?)
Total Weight	420 lbs. (191 kg)
Explosive Charge	290 lbs. (132 kg) TNT
Sink Rate / Terminal Velocity	9.9 fps (3.0 mps)
Settings	300 feet (91 m) max, later units 500 feet (182 m)
Notes: The standard DC of the first three years of World War II.

Mark VII Heavy .

Date Of Design	N/A
Date In Service	1940
Total Weight	420 lbs. (191 kg)
Explosive Charge	290 lbs. (130 kg) TNT
Sink Rate / Terminal Velocity	16.8 fps (5.1 mps)
Settings	300 feet (91 m) max
Notes: This had a 150 lbs. (68 kg) cast-iron weight attached to increase the sinking rate. The British claimed this DC would split a 0.875 inch (22 mm) hull at 20 feet (6.1 m) and force a submarine to surface at about twice that distance. A minol charge introduced in 1942 increased these distances to 26 feet (7.9 m) and 52 feet (15.8 m), respectively.

Mark VII Airborne DC .

Date Of Design	N/A
Date In Service	1941
Total Weight	450 lbs. (204 kg) (including fairings)
Explosive Charge	290 lbs. (132 kg) TNT
Sink Rate / Terminal Velocity	9.9 fps (3.0 mps)
Settings	about 25 feet (7.6 m)
Notes: A conversion of the standard Mark VII for aircraft use. Used nose and tail fairings that broke off when the DC hit the water. Could not be used at speeds over 150 knots and altitudes above 150 feet (46 m).

Mark VIII Airborne DC .

Date Of Design	1941
Date In Service	1942
Total Weight	246 lbs. (111.6 kg)
Explosive Charge	170 lbs. (77 kg) Torpex
Sink Rate / Terminal Velocity	N/A
Settings	25 feet (7.6 m)
Notes: Aircraft dropped DC. Designed to fit standard 250 lbs. (113 kg) bomb racks. Maximum drop limits of 750 feet (229 m) and 173 knots. Had a terminal velocity of 600 fps (183 mps).

Mark IX .

Date Of Design	N/A
Date In Service	N/A
Total Weight	about 420 lbs. (191 kg)
Explosive Charge	300 lbs. (136 kg) TNT
Sink Rate / Terminal Velocity	N/A
Settings	N/A
Notes: Magnetic fuzed. Not introduced into service.

Type L .

Date Of Design	N/A
Date In Service	N/A
Total Weight	about 420 lbs. (191 kg)
Explosive Charge	about 250 lbs. (113 kg) Minol
Sink Rate / Terminal Velocity	N/A
Settings	N/A
Notes: Magnetic fuzed. Not introduced into service.

Mark X, X* and X** .

Date Of Design	1941
Date In Service	1942
Total Weight	3,050 lbs. (1,383 kg)
Explosive Charge	2,000 lbs. (907 kg) TNT
Sink Rate / Terminal Velocity	Mark X: 6 fps (1.8 mps) Mark X: 21 fps (6.4 mps) Mark X*: 50 fps (15.2 mps)
Settings	Mark X: 220 feet (67 m) Mark X: 640 feet (195 m) Mark X*: Depths down to 1,500 feet (457 m)
Notes: Intended for launching from a 21 inch (53.3 cm) torpedo tube. The slow sinking speed of the Mark X was so that the launching ship could get clear of the explosion. In 1943, the Mark X* was introduced. This had a faster sinking and deeper depth setting intended to combat the deeper diving U-boats that were becoming more prevalent. In 1945, the even faster sinking Mark X** was developed for use against the newer, deeper diving U-boats, but this version was not introduced into service, as the ahead throwing weapons had obsoleted it.

Mark XI Airborne DC .

Date Of Design	1941
Date In Service	1942
Total Weight	246 lbs. (111.6 kg)
Explosive Charge	170 lbs. (77 kg) Torpex
Sink Rate / Terminal Velocity	N/A
Settings	25 feet (7.6 m)
Notes: An improved Mark VIII with a concave nose to reduce ricochets. Eventual limits were 1,250 feet (381 m) and 250 knots.

Mark XII .

Date Of Design	N/A
Date In Service	N/A
Total Weight	N/A
Explosive Charge	55 lbs. (25 kg) Minol
Sink Rate / Terminal Velocity	N/A
Settings	N/A
Notes: A small charge for use against midget submarines and similar devices.

Mark XIII .

Date Of Design	N/A
Date In Service	N/A
Total Weight	N/A
Explosive Charge	124 lbs. (56 kg) Minol
Sink Rate / Terminal Velocity	N/A
Settings	N/A
Notes: A larger version of the Mark XII for coastal forces. Also could be used against pursuing ships, somewhat similar to drifting mines.

Mark XIV Airborne DC .

Date Of Design	1941
Date In Service	1942
Total Weight	246 lbs. (111.6 kg)
Explosive Charge	170 lbs. (77 kg) Torpex
Sink Rate / Terminal Velocity	N/A
Settings	19 feet (5.8 m)
Notes: A further improvement of the 250 lbs. (113 kg) airborne depth charge. Not accepted by the RAF and cancelled in 1945.

Mark XV Airborne DC .

Date Of Design	1941
Date In Service	1942
Total Weight	246 lbs. (111.6 kg)
Explosive Charge	170 lbs. (77 kg) Torpex
Sink Rate / Terminal Velocity	N/A
Settings	See notes
Notes: Intended for use against schnorkel equipped U-boats. Had two pistols, one set for 20 feet (6.1 m) and the other for 50 feet (15 m). Not accepted into service by the RAF and cancelled in 1945.

Depth Charge Racks . Standard .

The first Depth Charge Rack in British service was the USN Mark I, which was developed after the USN rejected the British practice of using a sling to hold a single DC. Developed with help from Lt.Cmdr. Ishwood, RN, deliveries of the Mark I started in April of 1918 and 250 American, British and French destroyers had them installed by the Armistice.

Mark Numbers for other British DC Racks are not available at this time. Generally similar to USA versions, see USA ASW for further information. Racks manufactured in 1943-44 for escort vessels held 12, 18 or 34 charges.

Depth Charge Projectors . Mark I and Mark II Thornycroft .

Thornycroft DCT
Exposition of Navy Museum, Gdynia
Photograph copyrighted by Michal Kopacz

Development of this thrower started in 1916 and saw general service issue by August of 1917. Nominal range of 40 yards (27 m) when using the Type D depth charge. Sometimes listed as ML 9.5 in (24.1 cm) DCLT IV.

The British experienced production difficulties with this weapon and turned to the USA for help. When examined by the USN in 1917, the conclusion was that it was overengineered and the USN instead designed their own DCT, the famous "Y" gun.

Mark III .

USA's "Y" gun used on various Lend-Lease and USA-refitted ships. See USA ASW for details.

Mark IV .

Piston-type with non-expendable arbor. Nominal Range of 67 yards (61 m) for the Mark VII DC and 51 yards (47 m) for the Mark VII Heavy. In service 1941. Like the Mark II, this is sometimes listed as ML 9.5 in (24.1 cm) DCLT IV.

Mark V .

Replacement for the Mark IV. Piston-type with non-expendable arbor. Nominal Range of 78 yards (71 m) for the Mark VII DC and 62 yards (57 m) for the Mark VII Heavy. In service 1944. Sometimes listed as ML 6 in (15.2 cm) DCT Mark V.

USA Mark 6 .

Mark 6 K-gun Projector
Small handwheel opens breech for insertion of firing charge. The small tube on the right-hand side of the handwheel holds the percussion igniter. The chain around the depth charge holds it to the arbor.
The depth charges are probably USA Mark 6.
USN Photograph

The famous USA "K" gun. Used on Lend-Lease ships. Modified to handle British DCs. Fired a single Mark VII or Mark VII Heavy to ranges of 68 yards (62 m) and 55 yards (50 m) respectively. See USA ASW for other details.

Ahead-Throwing Weapon Projectors . 5" (12.7 cm), 7.5" (19 cm) and 11" (28 cm) Howitzers .

7.5" (19 cm) Howitzer

First issued in June 1917, these were short-barreled, rifiled howitzers that fired a projectile that looked much like a conventional artillery round. The projectiles used a special fuze that delayed detonation for two seconds after impact, which would allow them to sink about 20 feet (6 m). The round was designed to penetrate the outer casing of a U-Boat and then detonate on contact with the pressure hull. The 7.5" (19 cm) howitzer fired two types of projectiles. The first was a 100 lbs. (45 kg) projectile with a 43 lbs. (19.5 kg) charge with a maximum range of 2,100 yards (1,920 m) while the second was a 500 lbs. (227 kg) projectile with a 250 lbs. (113 kg) charge and a maximum range of 300 yards (275 m). In June 1918, the British modified both projectiles to add a flat nose disk that caused the rounds to dive at a steeper angle.

Issued primarily to Auxiliary Patrol Vessels with 42 being equipped by October 1917 and 174 by October 1918. The mountings had a limited traverse, probably because of concerns about the recoil blow. Not an effective weapon and no success are recorded.

3.5" (8.8 cm), 6" (15.2 cm), 7.5" (19 cm), 10" (25.4 cm) and 13.5" (34 cm) Bomb Throwers .

These were smooth-bore weapons that were the direct ancestor of the Thornycroft DCT and issued mainly to Special Service Vessels (small trawlers). All of these Bomb throwers fired directly ahead, there was no provision for traversing. These fired stick bombs using a hydrostatic fuze that could be set for 40 feet, 90 feet, 140 feet or 190 feet (12 m, 27 m, 43 m or 58 m). The 3.5" (8.8 cm) bomb thrower fired a 200 lbs. (91 kg) stick-bomb with a charge of 98 lbs. (44 kg) to a range of 1,200 yards (1,100 m) or a 350 lbs. (159 kg) stick-bomb with a charge of 200 lbs. (91 kg) to a range of 650 yards (590 m). Not an effective weapon and no success are recorded.

The British also developed a stick bomb for 12-pdr. guns on Auxiliary Patrol with each gun receiving four rounds. Used a similar hydrostatic fuze as the other stick bombs with the same four settings.

Hedgehog .

Mark 11 Hedgehog projector on the South Korean ship Apnok (formerly the USA PF-48) in December 1950
The motors at the front of the mount compensate for ship roll, the plate at the rear is a blast shield
USN Photograph

This 24-spigot mortar was the first ahead-throwing anti-submarine weapon in British service. More popular and more successful with the USN than with the Royal Navy, possibly because of the former's better sonar detection practices. Testing took place with a dummy installation on HMS Westcott in 1941 and production began in late 1942. No U-boats were sunk with the new weapon until November 1942 and it was not really successful in the Royal Navy until 1944 when improved sonar techniques were introduced.

Projectiles had a diameter of 7 inches (18 cm) and weighed 65 lbs. (29.5 kg) with an explosive charge of 35 lbs. (15.9 kg) of Torpex. Sinking speed was 22 to 23.5 fps (6.7 to 7.2 mps). The projectiles were angled to give a circular pattern 40 yards (37 m) in diameter about 200 yards (183 m) ahead of a stationary ship.

A variation was "Split Hedgehog" which was used in some sloops and other small ships where it was necessary to retain the forward gun. These mountings held 12 projectiles each and one was placed on each beam, near the bridge. These were coupled together, initially with wire ropes, later by hydraulic jacks. About 35 ships were so fitted between 1942 and 1943.

Parsnip .

Two ten-barrel units each firing a semi-circular pattern with a common center. Not in service.

Squid .

Literally ordered directly from the drawing board, this weapon was rushed into service in 1943 onboard HMS Ambuscade. This weapon was a three-barrel 12 inch (30.5 cm) mortar with the mortars mounted in series, one behind the other. The barrels were mounted in a frame that could be rotated 90 degrees for loading. The projectiles weighed 390 lbs. (177 kg) with a 207 lbs. (94 kg) minol charge. Sinking speed was 43.5 fps (13.3 mps) and a clockwork time fuze was used to set the depth. Maximum depth was 900 feet (274 m) and all three projectiles had to be set the same.

The weapons were automatically fired from the sonar range recorder at the proper moment. The pattern formed a triangle about 40 yards (37 m) on a side at a distance of 275 yards (250 m) ahead of the ship. The first successful use was by HMS Loch Killin on 31 July 1944, when she sank U-333.

Shark .

Developed very late in the war, this projectile could be fired by any 4 inch (10.2 cm) QF gun. Most guns used a propellant charge of 1.44 lbs. (0.65 kg) SC048, except for the Mark XVI* which used a charge of 1.63 lb (0.74). The Shark projectile weighed a total of 96.25 lbs. (43.66 kg) including a Torpex bursting charge of 24 lbs. (10.9 kg). Overall length was a maximum of 73.66 inches (187.1 cm) of which 53.3 in (135.9 cm) was the body and the rest finned tail. There were two anti-ricochet nose rings and a base percussion fuze. This weapon was intended to be fired to land 20 yards (18 m) short of the target submarine, strike the water and then continue its trajectory underwater to the hull. It was able to pierce any side tanks and then detonate in contact with the pressure hull. The outfit was to be 12 to 22 rounds per ship. It is not known if this was ever used against a U-Boat, but trials with it were thought to be "highly satisfactory."

Limbo .

Three-barrel mortar, somewhat similar to Squid. Limbo was the final development of British World War II ahead throwing ASW weapons. Range was controlled by opening gas vents and was between 400 and 1,000 yards (366 and 910 m). The barrels were aimed by a combination of roll and pitch compensators which also stabilized the mounting. This weapon was designed such that the shells always entered the water at the same angle, which simplified the fire control solution. The shells were time fuzed and used 207 lbs. (94 kg) minol for the explosive charge. Total weight was 390 lbs. (177 kg) and lethal range was about 5 yards (4.6 m). This weapon survived until the 1990s in the Royal Navy and Commonwealth Navies.

A Limbo mounting including a magazine holding 17 salvos (51 projectiles) weighed about 35 tons.

Photographs .

. Images at The Vickers Photographic Archive

See Depth Charges
See Limbo

Data from
"Naval Weapons of World War Two" by John Campbell
"US Naval Weapons" and "The Naval Institute Guide to World Naval Weapon Systems 1991/92" both by Norman Friedman
"Find and Destroy: Antisubmarine Warfare in World War I" by Dwight R. Messimer
"The U-Boat Offensive 1914-1945" by V.E. Tarrant