Hedgehog (weapon)
In 1941, a secret test aboard the destroyer HMS Starling revealed a fatal flaw in existing anti-submarine tactics. The Fairlie Mortar had failed to deliver results, leaving the Royal Navy desperate for a new solution. Lieutenant Colonel Stewart Blacker's spigot mortar design offered a fresh path forward. This weapon fired projectiles ahead of a ship instead of dropping them over the stern. The principle seemed viable despite earlier failures. The Directorate of Miscellaneous Weapons Development began adapting Blacker's infantry trench mortar for naval use. Major Millis Jefferis brought the Army's design into service with the Navy. They named the device after the animal whose spines resembled the empty rows of its launcher spigots. The system was designed to solve a specific problem: the target submarine disappearing from sonar when too close. Sound travels fast in water, creating an instantaneous echo that merged with the initial pulse. Operators could not distinguish the return signal while the submarine remained within depth-charge range. A submarine in this blind spot became effectively invisible to the sonar.
The Hedgehog employed contact fuzes rather than time or bathymetric fuzes. Detonation occurred directly against a hard surface such as the hull of a submarine. This made it more deadly than depth charges which relied on damage caused by hydrostatic shockwaves. An unsuccessful attack did not hide the submarine from sonar. When a depth charge exploded, it took 15 minutes before the disturbance settled enough for sonar to become effective again. Many submarines escaped during that window. Since Hedgehog charges exploded only on contact, sonar tracking of the submarine was less likely to be disrupted by an unsuccessful attack. There was no blind period allowing the submarine to escape undetected until depth-finding sonar arrived. The Royal Navy's Q attachment appeared in 1943 to address earlier limitations. U-boat commanders had become adept at sharp course changes during the final moments before a depth-charge attack began. They used direction speed to break contact and escape. The Hedgehog remained usable while the submarine was detectable by sonar giving it no time to take evasive actions.
Initial success rates hovered around five percent, only slightly better than depth charges. Swells and spray frequently covered the launcher during heavy North Atlantic weather. Subsequent attempts to launch from the soaked launcher were often hindered by firing circuit problems. Crews launched incomplete patterns when conditions turned rough. A depth charge total miss still produced an explosion leading crews to think they might have damaged their target. A Hedgehog miss was discouragingly quiet. The Royal Navy launched Hedgehog so seldom in early 1943 that a directive ordered captains to report why they had not used the weapon on underwater contacts. Results were blamed on crew inexperience and low confidence in the weapon. An officer from the DMWD traveled to Londonderry where escort vessels were based. Better training and shipwide talks on examples of successful attacks followed. By the end of the war statistics showed one in every five attacks made by Hedgehog resulted in a kill. This compared with fewer than one in eighty for depth charges. Out of 5,174 British depth charge attacks there were 85.5 kills. The Hedgehog made 268 attacks for 47 kills.
The mounting initially was fixed but later replaced by a gyro-stabilised version. This allowed for the rolling and pitching of the attacking ship during combat operations. The launcher had four cradles each containing six launcher spigots. The firing sequence was staggered so all bombs landed at about the same time. This minimized stress on the weapon's mounting so deck reinforcement was not needed. The weapon could be easily retrofitted at any convenient place on a ship. Reloading took about three minutes. The projectiles would sink at about two feet per second. They reached a submerged U-boat at 300 yards in under nine seconds. Sympathetic detonation of projectiles near those contacting hard surfaces was possible though usually fewer explosions counted than projectiles launched. The Mark 15 variant mounted the system on a platform adapted from that of a quadruple 40 mm Bofors gun mount. It could be fired remotely from the ship's plotting room.
In 1949, a copy of the Hedgehog was created in the USSR called the MBU-200. That design developed into the MBU-600 with an increased range of 200 meters. The United States produced a rocket version called Mousetrap then Weapon Alpha as a replacement for both. Still, the Hedgehog remained in service with the United States Navy into the Cold War until replaced by ASROC. Weapons derived from the Hedgehog have been largely phased out from Western navies in favor of homing torpedoes. In Russia and allied states like India they used anti-submarine rocket launchers like the RBU-6000. Three Hedgerow flotillas of specialized Landing Craft Assault boats carried the Hedgehog instead of troops during the Normandy landings. Impact fuse extensions enabled detonating warheads above ground to clear 100-yard-wide paths through mines. The Australian Army adapted the marine Hedgehog into a land-based seven-shot launcher mounted on Matilda tanks. By 1955 the Limbo system launched Minol charges replacing earlier mortar designs.
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Common questions
What is the Hedgehog weapon and when was it developed?
The Hedgehog weapon is a 1940s shipboard multi-barrel anti-submarine mortar of British origin. It was developed in 1941 by Lieutenant Colonel Stewart Blacker and adapted for naval use by Major Millis Jefferis.
How does the Hedgehog weapon differ from depth charges regarding sonar detection?
The Hedgehog weapon uses contact fuzes that detonate only upon hitting a hard surface, unlike depth charges which rely on hydrostatic shockwaves. This design prevents the blind period where submarines escape undetected after an explosion because unsuccessful attacks do not disrupt sonar tracking.
When did the Royal Navy begin using the Hedgehog weapon operationally?
The Royal Navy began operational use of the Hedgehog weapon in 1943 with the introduction of the Q attachment. Initial success rates hovered around five percent before training improvements increased effectiveness to one kill per every five attacks by the end of the war.
Who designed the original spigot mortar used for the Hedgehog weapon?
Lieutenant Colonel Stewart Blacker designed the original spigot mortar that formed the basis of the Hedgehog weapon. The Directorate of Miscellaneous Weapons Development adapted his infantry trench mortar design for naval application under the direction of Major Millis Jefferis.
What happened to the Hedgehog weapon after World War II ended?
The United States Navy kept the Hedgehog weapon in service until replaced by ASROC during the Cold War. A Soviet copy called the MBU-200 was created in 1949 and later evolved into the MBU-600, while Western navies eventually phased out these weapons in favor of homing torpedoes.