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Hedgehog


Photograph of antisubmarine Hedgehog

Imperial War Museum. Via Wikipedia Commons.


Specifications:


Number of projectiles     
24
Projectile diameter
7"
177.8mm
Projectile weight
65 lbs
2.5 kg
Explosive weight
35 lb
15.9 kg
Sinking speed
22-23.5 feet per second
6.7-7.2  meters per second
Range
200 yards
180 meters
Pattern
40 yard circle
37 meter circle

Hedgehog was an antisubmarine weapon developed by the British during the Second World War.  It was a large array of spigot mortars that could be fired ahead or to the sides of a warship.  The mortar shells fell in a large pattern over the area in which a submarine was thought to be lurking, with a sufficiently dense pattern that at least one or two shells would hit the submarine as they sank through the water.  Each shell carried a charge of about 60 pounds of high explosive, enough to seriously damage a submarine hull in contact.  Unlike depth charges, the hedgehog shells did not go off unless they scored a hit. 

Part of the impetus for developing Hedgehog was the fact that sonar-equipped ships of the Second World War could not maintain contact with a submarine that was almost directly beneath them.  This meant that a warship making a normal depth charge run lost track of its target at the very time it was supposed to drop depth charges, giving the submarine an opportunity to evade.  The first Hedgehogs were fired from a fixed mount over the bow of the ship before contact with the submarine was lost.  Later versions could be trained up 20 degrees port or starboard, giving considerably tactical flexibility.

Hedgehog was not without its flaws. Because of the relatively small explosive charge of the projectiles, a hit was not always immediately lethal. Nor was Hedgehog very effective against deep submarines, and conventional depth charges were preferred if the target was below 400 feet (120 meters) or sonar conditions were poor. Another problem was the limited number of reloads: While destroyers typically carried a large number of depth charges, the Hedgehog loadout was typically just seven patterns. The first Hedgehog kill did not take place until November 1942, and the best tactics for its effective use were not worked out until 1944. The first Hedgehog kill in the Pacific was of I-175 on 5 February 1944. Thereafter Hedgehog became an effective antisubmarine weapon, destroying the target in about 20 percent of attacks in the Atlantic (versus 6 percent of depth charge attacks in the same theater.)

Hedgehog was carried by all U.S. destroyer escorts, frigates, and older destroyers assigned to escort duty, but not by fleet destroyers. It was quite heavy and was considered suitable only for dedicated antisubmarine platforms.

Mousetrap was a similar American-designed weapon that eliminated the severe recoil of the spigot mortars by using rocket propulsion to launch Hedgehog warheads. A Mousetrap consisted of two to four sets of four rails for a total of eight to sixteen projectiles. It was not as effective as Hedgehog but could be used on smaller warships such as submarine chasers.

Hedgehog was being replaced as the war in the Pacific was winding down with the Squid advanced depth charge thrower.

References

Campbell (1985)

Carpenter and Polmar (1986)

Friedman (2004)
Keegan (1988)

Navweaps.com (accessed 2011-3-12)

Roscoe (1953)



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