Mk.10 Hedgehog mortar

Starboard Mk.10 Hedgehog mortar on Harukaze launching a nearly 30 kg depth charge with over 25 kg explosive filler

Description

The Hedgehog mortar is an anti-submarine weapon developed by the Royal Navy during World War 2. The weapon consists of 24 spigot projectiles that are fired from a mortar launcher, ahead of the ship. It is mounted on destroyer escorts or corvettes alongside conventional depth charges.

Vehicles equipped with this weapon

Vehicles equipped with this weapon
Motor gun boats	USS Candid
Gunboats
Britain	HMS Spey
Italy	Albatros
Frigates
USA	USS Hoquiam · USS Coolbaugh
Japan	Akebono · Ikazuchi · JDS Ayanami (DD-103)
Destroyers
Britain	HMS Churchill · HMS Montgomery
Japan	JDS Harukaze (DD-101)
Italy	Geniere
Heavy tanks	Matilda Hedgehog

General info

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Effective damage

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Comparison with analogues

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Usage in battles

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Pros and cons

Pros:

• The mortar fires on an high angle, which means it can reach hidden targets behind obstacles that block your guns
• Increased range compared to conventional depth charges.
• Can also obliterate enemy ships if it lands on the decks, dealing heavy damage.

Cons:

• Due to the high angle of fire, it has a curved trajectory and thus it takes a short while to hit the water.
• The mortar is fixed in position, which means it cannot traverse horizontally or vertically.
• The mortar is inaccurate: spigot projectiles spread out on a large area. Several projectiles are needed to secure a hit.

History

Background

The Royal Navy developed the first depth charges during World War I. Entering service in 1916, they tested a variety of methods of launching them off the ships and against German U-boats. These methods from rolling them off the boat to using trench mortars. Even with all the methods tested, the biggest limitation was that they required the U-boat to be underneath the ship to be used against them. During the inter-war period, the Royal Navy attempted to rectify this handicap by developing forward-firing anti-submarine warfare weapons with the Hedgehog Mortar being the first such weapon to enter service during World War II.

Named for the quill-like arrangement of the projectiles the Hedgehog was developed to fix the existing flaws interwar naval engineers noticed in anti-submarine warfare capabilities. Sonar was developed to find and destroy enemy submarines, but there was a blind spot immediately ahead and below the ship. The solution was to fire an overwhelming volume of explosive charges with contact detonators in this blind spot to destroy the sub. Development began during the war after the failure of the similar Fairline Mortar which like the earlier side launching Thronycroft projectors were too heavy for accurate targeting. The depth charges designed for it also 20 pounds of explosive filler instead of the desired 60 pounds. The Directorate of Miscellaneous Weapon Development (DMWD) built the Hedgehog as a spigot mortar to address the issues of weight and complexity. The British Army had already designed a spigot mortar called the Blacker Bombard primarily for use by the Home Guard as a cheap anti-tank weapon, so the Bombard design was quickly adapted for ASW to create the Hedgehog, a process done by Ministry Intelligence Research (MIR(c)) under Major Millis Jefferies.

Service

The Hedgehog was made in a variety of different variants with the Mark 10 serving as the base model in service. The Mark 10 fired 24 salvos that landed in an elliptical pattern about 140 by 120 feet and had a range of up to 200 yards. Originally used on a fixed mounting for the prototype mounted on the W-class destroy HMS Westcott in 1941, the production versions of the mortar had a gimbal mount to compensate for the ship’s roll. The Hedgehog system’s benefits over depth charges included the fact the ship could attack while still maintaining sonar contact and not disrupting the contact, the contact detonators removed the need to set the explosives to explode at a specific depth, and the contact detonators meant that a direct hit was more likely to sink a submarine. The mortar projectiles were 7.1 inches and weight 65 pounds each with a 35-pound Torpex (42% RDX, 40% TNT, 18% Powdered Aluminum) explosive warhead.

The Royal Navy first recorded sinking U-boats with the Hedgehog in November 1942 less than a year after it was introduced. Despite having a slightly higher kill rate than the depth charges in service, the Hedgehog was hampered by the violent nature of the North Atlantic causing the weapon to fail when exposed to sprays on the deck of the ships it was used. The kill rate soon improved to 1 in 5 Hedgehog attacks (by contrast to 1-in-80 with depth charges) after ship-wide talks and briefings of proper Hedgehog attacks at HMS Ferret, Londonderry, Northern Ireland. The Hedgehog Mortar was so successful that in response, the Kreigsmarine (German Navy) developed the G7e/TIV Falke (Falcon) homing acoustic torpedo to attack Allied convoys undetected. In the Royal Navy, the Hedgehog was replaced after the war with the Limbo mortar which fired 400-pound explosive charges.

Foreign Use

Along with service in the Royal Navy, the Hedgehog Mortar saw action in other Allied Navies through Lend-Lease and in other roles. In the Pacific Theater, the Buckley-class destroyer escort USS England had an unparalleled record of sinking six Imperial Japanese Navy submarines in 12 days using the Hedgehog Mortar. During the Normandy Landings in June 1944, the US had modified "Hedgerow" LCAs (Landing Craft, Assault) that cut 100-yard swathes through the German defenses. In addition, the Commonwealth forces used the Hedgehog with the Matilda Hedgehog being a notable Australian prototype variant of the mortar system mounted on a Matilda infantry tank as a bunker-buster weapon. While successful, the design never saw active service due to the end of the war. The United States and Soviet Navies both received the Hedgehog and developed their own similar weapons. The US Navy would develop the 7.2 in Mousetrap rockets and the Mark 108 "Weapon alfa" which saw service both during the war and in the post-war period. The Soviet Navy and the later Russian Navy keeps RBU-6000 and similar ASW mortars based on the Hedgehog design in service well after these designs were phased out by ASW rockets during the Cold War in other navies.

Media

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See also

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• reference to the article about the variant of the weapon;
• references to approximate analogues by other nations and research trees.

External links

• [Wikipedia] Hedgehog (weapon)
• [NavWeaps] United Kingdom / Britain: ASW Weapons
• [NavWeaps] United States of America: ASW Weapons
• [USS Slater] HEDGEHOG

References

Bibliography