Hedgehog (weapon)
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- 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 1943.
Hedgehog was replaced by the more effective Squid mortar in 1943 and this in turn was replaced by the three-barreled Limbo. The United States produced a similar weapon called Mousetrap.
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.
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[edit] Description
Technically the weapon was what is called a 'spigot-mortar' or spigot discharger, a type of weapon invented by Lt-Col Blacker, RA. That is 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 alternative is the common infantry trench-mortar which is basically a tube and the bomb is dropped down inside the tube firing the propelling charge when it hits bottom.
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 that 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:
- 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.
- 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'.
- The weapon gives no warning of the attack.
- Until depth-determining 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.
- A direct hit by 1-2 Hedgehog bombs was usually all that was needed 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.
The Hedgehog was much more successful than depth-charge attacks eventually (the best kill rate was about 25% of attacks whereas depth-charge attacks never got better than 7%). It initially had a very poor record although many of the factors had nothing to do with the design of the weapon.
[edit] 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)
[edit] 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.
[edit] See also
- Hedgerow, a land version of Hedghog for exploding landmines as used on Landing Craft during the D-Day invasion.
- The Blacker Bombard and PIAT infantry anti-tank weapons and the Churchill AVRE's Petard demolition gun also use the spigot discharger principle.
