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Hedgehog (weapon)

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Hedgehog anti-submarine weapon, British WWII
Hedgehog anti-submarine mortar with full load of practice bombs, circa 2002.
For the area denial weapon, see Czech hedgehog.

The Hedgehog was an anti-submarine weapon developed by the Royal Navy during World War II, that was deployed on convoy escort warships such as destroyers to supplement the depth charge. The weapon worked by firing a number of small spigot mortar bombs from spiked fittings. Rather than working on a time or depth fuse like depth charges, the bombs exploded on contact and achieved a higher sinking rate against submarines than depth charges did.

Hedgehog received its name because when unloaded, the rows of empty spigots resembled the spines of a hedgehog.

Hedgehog, also known as an Anti-Submarine Projector was developed by the Directorate of Miscellaneous Weapons Development and entered service in 1942.[1]

Hedgehog was replaced in new construction for the Royal Navy by the more effective Squid mortar in 1943. Squid was in turn replaced by the three-barreled Limbo. The United States produced a rocket version of Hedgehog called Mousetrap. The United States developed Weapon Alpha as a replacement for Hedgehog and Mousetrap. Hedgehog remained in service with the United States Navy into the cold war until both Hedgehog and the less satisfactory Weapon Alpha were replaced by ASROC.[2]

The Hedgehog was adapted into a 7 shot launcher form for use on the back of the Matilda tank serving with Australian forces.

From 1949, a copy of Hedgehog was produced in the USSR as MBU-200, developed in 1956 into MBU-600 with enhanced range of 600 m.

Description

Technically the weapon was what is called a 'spigot mortar' or spigot discharger, a type of weapon invented by Lt-Col Blacker, RA, and was the basis of early infantry trench mortars. The propelling charge was part of the main weapon and worked against a rod (the spigot) set in the baseplate which fitted inside a tubular tail of the 'bomb'. The tube style mortar where the bomb is dropped down inside the tube firing the propelling charge when it hits bottom was universally accepted by armies due to improved rates of fire and range. The WW2 British PIAT infantry anti-armour weapon was essentially a spigot mortar fired from the shoulder and some rifle grenades include elements of the spigot discharger/mortar concept.

The weapon fires a salvo of 24 bombs in an arc, aimed to land in a circular or elliptical area about 100 feet (30 m) in diameter at a fixed point about 250 yards (230 m) directly ahead of the attacking ship. The mounting initially was fixed but was later replaced by a gyro-stablised one to allow for the rolling and pitching of the attacking ship.

The launcher was 4 "cradles" each of 6 launcher spigots. The firing sequence was staggered so all the bombs would land at roughly the same time. This had the added advantage of minimising the stress on the weapon's mounting, so that deck re-inforcement was not needed, and the weapon could easily be retro-fitted to any convenient place on a ship. Reloading took about 3 minutes.

The Hedgehog had four key advantages over the depth charge:

  1. An unsuccessful attack does not hide the submarine from sonar.
    When a depth charge explodes it can take 15 minutes before the disturbance can settle down enough that sonar becomes effective. Many submarines escaped during the time after an unsuccessful depth charge attack. Since Hedgehog charges only explode on contact, if they miss, the submarine can still be tracked by sonar.
  2. The depth of the target does not need to be known.
    Proximity weapons (such as depth charges) need to be set for the target's correct depth to be effective. Contact fused charges don't have that limitation. In addition, any explosion indicates a 'hit'.
  3. The weapon gives no warning of the attack.
    Until depth-finding sonar became available (the first was the Royal Navy's 'Q' attachment in 1943), there was a 'dead period' during the final moments of the attack when the attacker had no knowledge of what the target was doing. U-boat commanders became adept at sharp changes of direction and speed at these moments, thus making the attack less accurate. Ahead-thrown weapons such as Hedgehog did not give the target the necessary warning of when to dodge.
  4. A direct hit by 1-2 Hedgehog bombs was usually sufficient to sink a submarine.
    Many depth charges were required in order to inflict accumulating damage sufficient to sink a submarine; even then, many U-boats survived hundreds of detonations over a period of many hours; 678 depth charges were dropped onto U 427 in April, 1945. The depth charge, being usually distanced from the submarine had a cushion of water between it and the target which rapidly dissipated the explosive shock. A contact charge, on the other hand, had the cushion on the other side actually increasing the explosive shock.

However the Hedgehog did not have the advantage of any cumulative damage effect of repeated explosions just outside the lethal distance that could make it harder for the target to dodge later attacks or force it to return to base for repairs when it did escape. Nor did it have the same psychological effect a depth charge attack did.

The Hedgehog was much more successful than depth charge attacks eventually (the best kill rate was about 25% of attacks whereas depth charge never achieved more than 7%). It initially had a very poor record although many of the factors had nothing to do with the design of the weapon. USS England sank six Japanese submarines in a matter of days with Hedgehog in May 1944.[3]

General characteristics

For a single bomb

  • Caliber: 7 in (178 mm)
  • Weight: 65 lb (29 kg)
  • Explosive charge: 30 lb TNT or 35 lb (16 kg) Torpex
  • Range: 200 to 259 m
  • Sinking speed: 22 to 23.5 ft/s (6.7 to 7.2 m/s)

Variants

  • Mark 10: elliptical pattern measuring about 140 x 120 feet to a range of 200 yards
  • Mark 11: circular pattern measuring 200 feet in diameter out to a range of about 188 yards.
  • Mark 15: pattern as for the Mark 11 but mounted on a platform adapted from that of a quadruple 40 mm Bofors gun mount. The Mark 15 could be fired remotely from the ship's plotting room.

See also

Notes

  1. ^ Fitzsimons, Bernard, ed. Illustrated Encyclopedia of 20th Century Weapons & Warfare (London: Phoebus, 1977), Volume 12, p.1283, "Hedgehog".
  2. ^ Albrecht, Gerhard. Weyer's Warship of the World 1969. (Annapolis, MD: United States Naval Institute Press, 1969), pp.325-328 & 340
  3. ^ Lanier, William D. and Williamson, John A., CAPT USN "The Twelve Days of the England" United States Naval Institute Proceedings March 1980 pp. 76-83
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