Hedgehog (weapon) - Description

Description

Technically the weapon was a multiple 'spigot mortar' or spigot discharger, a type of weapon developed in the interwar period by Lt-Col Blacker, RA. The spigot mortar was based on early infantry trench mortars. By using a spigot, the warhead and barrel size were no longer dependent in the design. 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'. This principle was first used on the Blacker Bombard and the later PIAT anti-tank weapon.

The adaptation of the bombard for naval use was made in partnership with MIR(c) under Major Millis Jefferis who had taken Blacker's design and brought it into use with Army. 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-stabilised one to allow for the rolling and pitching of the attacking ship.

The launcher had 4 "cradles", each with 6 launcher spigots. The firing sequence was staggered so all the bombs would land at about the same time. This had the added advantage of minimising the stress on the weapon's mounting, so that deck reinforcement was not needed, and the weapon could easily be retrofitted 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 or 2 Hedgehog bombs was usually sufficient to sink a submarine.

   Many depth charges were required in order to inflict enough cumulative damage to sink a submarine; even then, many U-boats survived hundreds of detonations over a period of many hours—678 depth charges were dropped against U 427 in April 1945. The depth charge, usually exploding at a distance from the submarine, had a cushion of water between it and the target which rapidly dissipated the explosive shock. The Hedgehog's contact charge, on the other hand, had the cushion on the other side, actually increasing the explosive shock. However near-misses with the Hedgehog did not cause cumulative damage as depth charges did; nor did it have the same psychological effect as a depth charge attack.

The Hedgehog became much more successful than depth-charge attacks (the best kill rate was about 25% of attacks whereas depth charges 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.