Hedgehog (weapon)

Last updated

Hedgehog anti-submarine mortar.jpg
On HMS Westcott, November 1945
TypeAnti-submarine mortar
Place of originUnited Kingdom
Service history
In service1942–?
Used byNaval Ensign of the United Kingdom.svg  Royal Navy
Flag of the United States.svg  United States Navy
Ensign of the United States Coast Guard.svg  United States Coast Guard
Naval Ensign of the United Kingdom.svg  Royal Canadian Navy
Production history
Designer Directorate of Miscellaneous Weapons Development
Designed1941 [1]
Shell 65 lb (29 kg) [1]
Calibre 7 in (178 mm) [1]
Barrels24 [1]
Effective firing range200–259 m (656–850 ft)
Filling30 lb (14 kg) TNT or 35 lb (16 kg) Torpex [1]

The Hedgehog (also known as an Anti-Submarine Projector) was a forward-throwing anti-submarine weapon that was used during the Battle of the Atlantic in the Second World War. The device, which was developed by the Royal Navy, fired up to 24 spigot mortars ahead of a ship when attacking a U-boat. [2] It was deployed on convoy escort warships such as destroyers and corvettes to supplement the depth charges.

Anti-submarine weapon

An anti-submarine weapon (ASW) is any one of a number of devices that are intended to act against a submarine and its crew, to destroy (sink) the vessel or reduce its capability as a weapon of war. In its simplest sense, an anti-submarine weapon is usually a projectile, missile or bomb that is optimized to destroy submarines.

Battle of the Atlantic longest continuous military campaign in World War II

The Battle of the Atlantic was the longest continuous military campaign in World War II, running from 1939 to the defeat of Nazi Germany in 1945, and was a major part of the Naval history of World War II. At its core was the Allied naval blockade of Germany, announced the day after the declaration of war, and Germany's subsequent counter-blockade. It was at its height from mid-1940 through to the end of 1943.

Royal Navy Maritime warfare branch of the United Kingdoms military

The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by the English kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years War against the Kingdom of France. The modern Royal Navy traces its origins to the early 16th century; the oldest of the UK's armed services, it is known as the Senior Service.


As the mortar projectiles employed contact fuzes rather than time or barometric (depth) fuzes, detonation occurred directly against a hard surface such as the hull of a submarine making it more deadly than depth charges, which relied on damage caused by hydrostatic shockwaves. Statistics show that during WWII out of 5,174 British depth charge attacks there were 85.5 kills: 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]

A contact fuze, impact fuze, percussion fuze or direct-action (D.A.) fuze (UK) is the fuze that is placed in the nose of a bomb or shell so that it will detonate on contact with a hard surface.

Depth charge anti-submarine weapon

A depth charge is an anti-submarine warfare weapon. It is intended to destroy a submarine by being dropped into the water nearby and detonating, subjecting the target to a powerful and destructive hydraulic shock. Most depth charges use high explosive charges and a fuze set to detonate the charge, typically at a specific depth. Depth charges can be dropped by ships, patrol aircraft, and helicopters.


The "Hedgehog", so named because the empty rows of its launcher spigots resembled the spines of a hedgehog, was a replacement for the unsuccessful Fairlie Mortar that was trialled aboard HMS Whitehall in 1941. Although a failure, the Fairlie was designed to fire depth charges ahead of a ship when attacking a submarine. This principle of forward-firing projectiles was considered viable. This secret research by the Directorate of Miscellaneous Weapons Development (DMWD) led to the development of the Hedgehog. [4]

Hedgehog subfamily of small spiny mammals

A hedgehog is any of the spiny mammals of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found through parts of Europe, Asia, and Africa, and in New Zealand by introduction. There are no hedgehogs native to Australia and no living species native to the Americas.

The Fairlie Mortar was an unsuccessful British anti-submarine mortar design of early World War II. It projected multiple small anti-submarine bombs simultaneously, 10 from each side of the ship's forecastle, each containing 20 pounds of explosive, but "Hedgehog" projecting 24 small bombs from a single platform eventually became the predominant British weapon in the war.

The weapon was a multiple 'spigot mortar' or spigot discharger, a type of weapon developed between the wars by Lieutenant Colonel Stewart Blacker, RA. The spigot mortar was based on early infantry trench mortars. The spigot design allowed a single device to fire warheads of varying size. 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 29 mm Spigot Mortar and the later PIAT anti-tank weapon.

Stewart Blacker British Army officer

Lieutenant-Colonel Latham Valentine Stewart Blacker OBE was a British Army officer and inventor of weapons; he invented the Blacker Bombard, from which was developed the Hedgehog anti-submarine spigot-mortar - and laid the basis of the PIAT anti tank weapon.

Royal Artillery artillery arm of the British Army

The Royal Regiment of Artillery, commonly referred to as the Royal Artillery (RA) and colloquially known as "The Gunners", is the artillery arm of the British Army. The Royal Regiment of Artillery comprises thirteen Regular Army regiments, King's Troop Royal Horse Artillery and five Army Reserve regiments.

Infantry military service branch that specializes in combat by individuals on foot

Infantry is a military specialization that engages in military combat on foot, distinguished from cavalry, artillery, and tank forces. Also known as foot soldiers or infanteers, infantry traditionally relies on moving by foot between combats as well, but may also use mounts, military vehicles, or other transport. Infantry make up a large portion of all armed forces in most nations, and typically bear the largest brunt in warfare, as measured by casualties, deprivation, or physical and psychological stress.

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 the 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.

Sir Millis Rowland Jefferis KBE MC was a British military officer who founded a special unit of the British Ministry of Supply which developed unusual weapons during the Second World War.

Circle simple curve of Euclidean geometry

A circle is a simple closed shape. It is the set of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves in a plane so that its distance from a given point is constant. The distance between any of the points and the centre is called the radius. This article is about circles in Euclidean geometry, and, in particular, the Euclidean plane, except where otherwise noted.

Ellipse Plane curve: conic section

In mathematics, an ellipse is a plane curve surrounding two focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant. As such, it generalizes a circle, which is the special type of ellipse in which the two focal points are the same. The elongation of an ellipse is measured by its eccentricity e, a number ranging from e = 0 to e = 1.

The system was developed to solve the problem of the target submarine disappearing from the attacking ship's ASDIC when the ship came within the sonar's minimum range. Due to the speed of sound in water, the time taken for the 'ping' echo to return to the attacking ship from the target submarine became too short to allow the human operator to distinguish the returning audible echo from that of the initial sound pulse emitted by the sonar – the so-called "instantaneous echo", where the output sound pulse and returning echo merge. This "blind spot" allowed the submarine to make evasive manoeuvres undetected while the ship was out of range for depth charge attack. Hence, the submarine was effectively invisible to the sonar as the ship came within the sonar's minimum range. The solution was a weapon mounted on the foredeck that discharged the projectiles up and over that carrying ship's bow, to land in the water some distance in front of the ship while the submarine was still outside the sonar's minimum range.

Forecastle upper deck of a sailing ship forward of the foremast

The forecastle is the upper deck of a sailing ship forward of the foremast, or the forward part of a ship with the sailors' living quarters. Related to the latter meaning is the phrase "before the mast" which denotes anything related to ordinary sailors, as opposed to a ship's officers.

Bow (ship) forward part of the hull of a ship

The bow is the forward part of the hull of a ship or boat, the point that is usually most forward when the vessel is underway. Both of the adjectives fore and forward mean towards the bow. The other end of the boat is the stern.


The Hedgehog entered service in 1942. Carrying a Torpex charge weighing 16 kg (35 lb), each mortar had a diameter of 18 cm (7.1 in) and weighed about 29.5 kg (65 lb). The projectiles were angled so they would land in a circular shape with a diameter of 40 m (130 ft) about 180 m (590 ft) ahead of a stationary ship. The projectiles would then sink at about 7 m/s (23 ft/s). [1] They would reach a submerged U-boat, for example at 200 ft (61 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 aboard HMS 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 often revealed firing circuit problems launching an incomplete pattern. [7] The disappointment of a quiet miss discouraged crews who might otherwise assume depth charge explosions had damaged their target or at least frightened the enemy. 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 had not 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 to Londonderry Port, where the convoy crews 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 to less than one in 80 with depth charges). [3]

In response to this new deadly threat to its U-boats, the Kriegsmarine brought forward its programme of acoustic torpedoes in 1943, beginning with the Falke. These new "homing" torpedoes could be employed effectively without the use of a periscope, providing submarines a better chance to remain undetected and evade counterattack.

In the Pacific Theater, USS England sank six Japanese submarines in a matter of days with Hedgehog in May 1944. [5]

In 1946, USS Solar was destroyed after a crewman accidentally dropped a Hedgehog charge near one of her main turret ammunition rooms, triggering three subsequent and devastating explosions.

Operational usage

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, and the weapon could easily be retrofitted to any convenient place on a ship. Reloading took about three minutes. [1]

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, sonar tracking of the submarine is less likely to be disrupted by an unsuccessful hedgehog attack.
  2. 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]
    Proximity weapons (such as depth charges) need to be set for the target's correct depth to be effective. Contact-fuzed charges do not have that limitation, and an explosion at the time predicted for the contact-fuzed projectile to reach the target depth may indicate a "hit". [10]
  3. The weapon gives no warning of the attack.[ citation needed ]
    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 one or two Hedgehog bombs was usually sufficient to sink a submarine.[ citation needed ]
    Many depth charges were required 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.[ citation needed ] 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.

Derivatives and successors

A hedgehog launcher on display at the USS Silversides museum in Muskegon, Michigan. A hedgehog launcher on display.jpg
A hedgehog launcher on display at the USS Silversides museum in Muskegon, Michigan.

In late 1943 the Royal Navy introduced Squid. This was 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-barreled Limbo that launched 400 lb (180 kg) Minol charges.

The United States produced a rocket version of Hedgehog called Mousetrap, then Weapon Alpha as a replacement for both. Still, Hedgehog remained in service with the United States Navy into the Cold War until both Hedgehog and the less satisfactory Weapon Alpha were replaced by ASROC. [12]

Three "Hedgerow" flotillas of specialized Landing Craft Assault boats carrying the Hedgehog instead of troops were used during the Normandy landings. [13] 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. [14] [15]

The Australian Army adapted the marine Hedgehog into a land-based seven-shot launcher that could be mounted on the back of Matilda tanks.

From 1949, a copy of Hedgehog was produced in the USSR as MBU-200, developed in 1956 into MBU-600 (also known as RBU-6000) with increased range of 600 metres (2,000 ft).

Weapons derived from the Hedgehog have been largely phased out from Western navies in favor of homing torpedoes. MBU-600 and its derivatives remain an important part of the Russian Navy's (as well as Russia's allies, such as India) anti-submarine arsenal to this day.

Former operators

General characteristics

Live and practice projectiles - note the protective fuze caps (22) shown removed in the picture at the top of page. Hedgehog ASW projectile diagram.jpg
Live and practice projectiles – note the protective fuze caps (22) shown removed in the picture at the top of page.

For a single bomb


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