| Hedgehog | |
|---|---|
 OnHMS Westcott, November 1945 | |
| Type | Anti-submarine mortar |
| Place of origin | United Kingdom |
| Service history | |
| In service | 1942 to ? |
| Used by | |
| Production history | |
| Designer | Directorate of Miscellaneous Weapons Development |
| Designed | 1941[1] |
| Specifications | |
| Shell | 65 lb (29 kg)[1] |
| Calibre | 7 in (178 mm)[1] |
| Barrels | 24[1] |
| Effective firing range | 656–850 ft (200–259 m) |
| Filling | 30 lb (14 kg) TNT or 35 lb (16 kg) Torpex[1] |
Detonation mechanism | Contact |
TheHedgehog (also known as anAnti-Submarine Projector) was a forward-throwinganti-submarine weapon that was used primarily during theSecond World War. The device, which was developed by theRoyal Navy, fired up to 24spigot mortars ahead of a ship when attacking aU-boat.[2] It was deployed onconvoy escortwarships such asdestroyers andcorvettes to supplement thedepth charges.
As the mortar projectiles employedcontact fuzes rather thantime orbathymetric (depth) fuzes, detonation occurred directly against a hard surface such as the hull of a submarine, making it more deadly thandepth charges, which relied on damage caused byhydrostatic shockwaves. During World War II out of 5,174 British depth charge attacks there were 85.5 kills,[a] a ratio of 60.5 to 1. In comparison, the Hedgehog made 268 attacks for 47 kills, a ratio of 5.7 to 1.[3]
The Hedgehog, so named because the empty rows of its launcher spigots resembled the spines on the back of ahedgehog, was a replacement for the unsuccessfulFairlie Mortar, which was secretly tested aboardHMS Whitehall in 1941. The Fairlie was designed to firedepth charges ahead of a ship when attacking a submarine. The principle of firing projectiles forwards, instead of dropping depth charges over the stern, was considered viable, despite the failure of the Fairlie. This research by theDirectorate of Miscellaneous Weapons Development (DMWD) led to the development of the Hedgehog.[4]
The weapon was a multiplespigot mortar, or spigot discharger, a type of weapon developed between the wars by Lieutenant ColonelStewart Blacker,RA. The spigot mortar was based on earlyinfantry trench mortars. The spigot design allowed a single device to fire warheads of different sizes. The propelling charge was part of the main weapon and worked against a rod (the spigot) set in a baseplate which fitted inside the tubular tail of the bomb. This principle was first used in theBlacker Bombard 1.1-inch (29 mm) Spigot Mortar, and it was also used in the laterPIAT anti-tank weapon.
The adaptation of the bombard for naval use was made in partnership withMIR(c) under MajorMillis Jefferis, who had taken Blacker's design and brought it into use with the Army. The weapon fires a salvo of 24 bombs in an arc, aimed to land in acircular orelliptical area about 100 feet (30 m) in diameter at a fixed relative location about 250 yards (230 m) directly ahead of the attacking ship. The mounting initially was fixed, but it was later replaced by a gyro-stabilised one to allow for the rolling and pitching of the attacking ship.
The system was developed to solve the problem of the target submarine disappearing from the attacking ship'sASDIC when closer than the sonar's minimum range. Thespeed of sound in water is such that the time taken for the ping echo to return to the attacking ship from a close-by target submarine is too short to allow the human operator to distinguish the returning audible echo from the initial sound pulse emitted by the sonar – the so-calledinstantaneous echo, where the output sound pulse and returning echo merge, with the submarine still out of depth-charge range. A submarine in this blind spot became effectively invisible to the sonar, allowing it to make evasive manoeuvres undetected. The solution was a weapon mounted on theforedeck that discharged the projectiles up and over the ship'sbow while the submarine was still detectable by the sonar, entering the water some distance in front of the ship.
The Hedgehog entered service in 1942. Carrying a 35 lb (16 kg)Torpex charge, each mortar projectile had a diameter of 7.1 in (18 cm) and weighed about 65 lb (29.5 kg). The spigots were angled so the projectiles would land in a circular pattern with a diameter of 130 ft (40 m), about 200 yd (180 m) ahead of the ship's position. The projectiles would then sink at about 23 ft/s (7 m/s).[1] They would reach a submerged U-boat, for example at 200 ft (60 m) in under 9 seconds.Sympathetic detonation of projectiles near those contacting hard surfaces was a possibility, but the number of explosions counted was usually fewer than the number of projectiles launched.[5]
The prototype launcher was tested aboardHMS Westcott in 1941, but there were no submarine kills until November 1942, after it had been installed aboard one hundred ships.[1] Initial success rates, of about 5%, were only slightly better than depth charges. Swells and spray frequently covered the launcher during heavy North Atlantic weather,[6] and subsequent attempts to launch from the soaked launcher were often hindered by firing circuit problems, launching an incomplete pattern.[7] A depth charge total miss would still produce an explosion, leading crews to think that they might have damaged their target or at least demoralised its personnel; a Hedgehog miss was discouragingly quiet. The Royal Navy launched Hedgehog so seldom in early 1943 that a directive was issued ordering captains of ships equipped with Hedgehog to report why they hadnot used Hedgehog on an underwater contact.[8] The results were blamed on crew inexperience and low confidence in the weapon. However, after an officer from the DMWD was sent tothe base at Londonderry, where the escort vessels were based, with better training and shipwide talks on examples of successful Hedgehog attacks, the kill rate improved considerably.[9] By the end of the war, statistics showed that on average, one in every five attacks made by Hedgehog resulted in a kill (compared with fewer than one in eighty with depth charges).[3]
In response to this new deadly threat to its U-boats, theKriegsmarine brought forward its programme ofacoustic torpedoes in 1943, beginning with theFalke. These new "homing"acoustic torpedoes could be employed effectively without the use of a periscope, providing submarines a better chance to remain undetected and evade counterattack.
In thePacific Theatre,USS England sank six Japanese submarines in a two-week period with the Hedgehog in May 1944.[5]
In 1946, the destroyer escortUSS Solar was destroyed while unloading ammunition when a crewman accidentally dropped a Hedgehog charge near one of her main turret ammunition rooms, triggering three devastating explosions that wrecked the superstructure.
The launcher had four "cradles", each with six 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, allowing the weapon to be easily retrofitted at any convenient place on a ship. Reloading took about three minutes.[1]
The Hedgehog had four key advantages over the depth charge:
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 explode only on contact, sonar tracking of the submarine is less likely to be disrupted by an unsuccessful Hedgehog attack.
However, although knowledge of target depth was less important, the Hedgehog was less successful against deep targets. Doctrine based on combat experience discouraged use on targets deeper than 400 feet (120 m).[1]
Untildepth-finding sonar became available (the first was the Royal Navy'sQ attachment in 1943), there was a "dead period" during the final moments before a depth-charge attack began when contact with the target would be lost. U-boat commanders became adept at sharp course changes and direction speed at these moments to break contact and escape. Hedgehog remained usable while the submarine was detectable by sonar giving it no time to take evasive actions.
Many depth charges were required to inflict enough cumulative damage to sink a U-boat; even then, many survived hundreds of detonations over a period of many hours. For example,U-427 survived 678 depth charges dropped against it in April 1945. The effectiveness of the depth charge was reduced because they detonated at a set depth at a distance away from the submarine, the explosive shock was rapidly dissipated by a cushion of water between it and the target. In contrast the Hedgehog charge exploded in direct contact with the hull.[11] However, misses with the Hedgehog were silent and did not cause any damage, unlike the cumulative damage caused by depth charging, nor did it have the same psychological effect as a depth charge attack.
![A large white upwelling of water from an underwater explosion just ahead of Moberly's bow following Hedgehog launch[12]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aU-853-sinking2.jpg)
_during_ASW_exercise_1950.jpg)
In late 1943, the Royal Navy introduced theSquid, a three-tubed mortar that launched depth charges. Initially it was used as a single weapon, but when this failed to be successful, it was upgraded to the "double squid" that consisted of two launchers placed in parallel. In 1955 this system was upgraded to the three-barrelledLimbo that launched 400 lb (180 kg)Minol charges.
The United States produced a rocket version of the Hedgehog calledMousetrap, thenWeapon Alpha as a replacement for both. Still, the Hedgehog remained in service with the United States Navy into theCold War until both it and the less satisfactory Weapon Alpha were replaced byASROC.[13]
Three "Hedgerow" flotillas of specializedLanding Craft Assault boats carrying the Hedgehog instead of troops were used during theNormandy landings.[14] An addition of impact fuse extensions in the projectile noses enabled detonating the warheads above ground. The bombs were used to clear 100-yard-wide paths through mines and barbed wire obstacles on the beach.[15][16]
The Australian Army adapted the marine Hedgehog into a land-based seven-shot launcher that could be mounted on the back ofMatilda tanks.
In 1949, a copy of the Hedgehog was created in theUSSR called the MBU-200, which was then developed in 1956 into the MBU-600 with an increased range of 704 yards (644 m).[17]
Weapons derived from the Hedgehog have been largely phased out from Western navies in favor ofhoming torpedoes, and in Russia and allied states like India by anti-submarine rocket launchers like theRBU-6000.
Royal Navy
Spanish Navy
United States Navy Royal Canadian Navy
United States Coast Guard
Philippine Navy
Royal Danish Navy
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