Hedgehog (weapon)

Hedgehog (weapon)
Royal Navy official photographer · Public domain · source
Name	Hedgehog
Caption	Forward-firing anti-submarine mortar system
Origin	United Kingdom
Type	Anti-submarine weapon
Service	1942–1960s
Used by	Royal Navy, United States Navy, Royal Canadian Navy, Royal Australian Navy, Royal New Zealand Navy
Wars	Second World War, Cold War
Designer	Admiralty
Design date	1941–1942
Manufacturer	Various contractors
Caliber	7-inch (nominal)
Range	275–1000 yards
Filling	Torpex, Minol
Detonation	Contact fuze

Hedgehog (weapon) was a forward-throwing anti-submarine mortar developed by the Royal Navy during the Second World War to improve convoy protection against U-boat attacks. It launched multiple small contact-fuzed projectiles ahead of a ship, allowing continuous sonar contact and a reduced missed-attack problem that plagued depth charge tactics used by HMS, Royal Canadian Navy and Royal Australian Navy escorts. The system influenced postwar anti-submarine warfare concepts adopted by United States Navy and NATO navies during the early Cold War.

Development and design

Development stemmed from research at Admiralty Research Establishment, influenced by lessons from the Battle of the Atlantic and signals from convoy escorts such as HMS Broadwater and escort groups led by commanders like Captain Frederic John Walker. Designers sought to replace stern-thrown depth charge patterns derived from interwar experiments with forward-throwing patterns inspired by ASDIC doctrine and antisubmarine trials involving HMS Westcott and trials at Portsmouth. Engineers at Admiralty and contractors including Vickers-Armstrongs and Armstrong Whitworth produced a spigot-launched mortar array that fired 24 to 48 spigot mortars in a salvo. The projectiles used contact fuzes developed from work at Woolwich Arsenal and explosive fills like Torpex and Minol to increase lethality against pressure hulls of Type VII U-boat and Type IX U-boat classes. The launcher’s pattern geometry was optimized using range-finding and fire-control inputs from ASDIC and later combined with direction-finding data from High-Frequency Direction Finding stations and convoy escort tactics refined by leaders such as Max Horton.

Operational history

Hedgehog first entered service aboard HMS Westcott and other escort sloops and corvettes in 1942 during operations protecting convoys in the North Atlantic, Mediterranean, and Arctic routes to Murmansk. Its debut correlated with improved kill rates against German Kriegsmarine U-boats during convoy battles like those involving convoy HX and SC series and antisubmarine sweeps by Western Approaches Command. Crews trained at HMS Osprey and shore bases in Scapa Flow learned integrated use with sonar platforms such as Type 144 and Type 147 and with airborne assets from squadrons of Fleet Air Arm and Royal Air Force Coastal Command. Hedgehog-equipped escorts claimed numerous successes against U-boat types and later influenced actions against S-boat and E-boat thermal threats in littoral zones. After VE Day the system remained in service with NATO allies and was adapted for postwar frigates and destroyer escorts during events like the Korean War before being superseded by ahead-throwing systems such as Squid and Limbo.

Tactics and effectiveness

Tactical doctrine emphasized maintaining sonar contact during attack runs, using Hedgehog to fire ahead of the ship rather than losing contact by passing over a target as with stern-borne depth charge patterns. Escort commanders integrated Hedgehog salvos with ASDIC echo interpretation, radar contact from sets like Type 271, and radio intelligence including Ultra decrypts in coordinated convoy defense. The contact-fuzed projectiles detonated only on impact, reducing disturbance of the water column and allowing rapid re-acquisition if the salvo missed—contrasting with the disruptive shockwaves of conventional depth charges that masked sonar returns. Hedgehog achieved higher first-attack kill probabilities against submerged U-boat targets and imposed tactical changes on Kriegsmarine commanders, who adjusted evasion tactics and depth profiles. Its limitations included dependence on accurate range and bearing from ASDIC, reduced effectiveness against deeply submerged targets beyond explosive charge depth ratings, and vulnerability in heavy sea states or when faced with evasive countermeasures.

Variants and international use

Variants included 24- and 48-spigot launchers fitted to escort vessels, adapted mountings for Flower-class corvette, River-class frigate, and frigate designs, and modifications for United States Navy production on Destroyer escort classes. Allied navies such as Royal Canadian Navy, Royal New Zealand Navy, Royal Australian Navy, and later Royal Netherlands Navy and French Navy incorporated Hedgehog or derivative systems into wartime and early Cold War fleets. Postwar evolution led to successors like Squid and Limbo developed at Admiralty establishments and installed on ships transferred under Lend-Lease or built for NATO partners including Italy, Greece, and Turkey. Some navies combined Hedgehog with rocket-assisted depth-charge projects and later homing torpedoes such as Mark 46 in multinational antisubmarine task groups during exercises under NATO command.

Technical specifications

- Launcher types: 24-spigot and 48-spigot arrays used on various escorts such as Flower-class corvette and River-class frigate. - Projectile: 7-inch diameter spigot-fuzed bomb with contact fuze; warhead filled with Torpex or Minol. - Weight and dimensions: shipboard mountings varied by class and manufacturer including Vickers-Armstrongs and Armstrong Whitworth fittings. - Range: effective engagement envelope typically 275–1000 yards depending on mounting and elevation, enabling ahead firing beyond ASDIC blind sectors. - Fuzing: impact-only contact fuzes developed at Woolwich Arsenal and tested at ranges such as Portsmouth and Scapa Flow. - Integration: fire-control linkage with ASDIC Type 144/147 sets, radar Type 271, and bridge control systems used in Royal Navy antisubmarine procedures.

Category:Anti-submarine weapons Category:Naval weapons of the United Kingdom