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Ahead Thrown Missiles: The Mark 10 projector, known as the Hedgehog, launches 24 - 7.2 inch missiles with contact fuzes.
Usual Range: 250 - 280 Yards/ 230-260 Meters
Rate of Fire: 1 Salvo per 3 minutes

Missile: The projector charge has a head of 7.2 inches in diameter, with a tail, fins and a shroud. This missile is not a rocket; the propelling charge is an impulse charge of smokeless powder. The fuze arms during flight and is designed to function upon impact only. The explosive charge consists of 30 pounds of TNT, or 35 pounds of Torpex.

Projector: Projector Mark 10, projects a pattern of 24 charges ahead of the attacking vessel. The missiles are loaded on cylindrical bars called spigots, six are attached to each cradle, with four cradles in the projector. These cradles are interconnected and can be swung about a fore-and-aft axis by means of a roll-correction gear assembly mounted on a gun-train indicator pedestal. This movement is limited, but allows enough movement to compensate for roll of the ship and to aid in leading the target. The spigots are so positioned that when fired the charges describe an elliptical pattern of about 140 by 120 feet, at an average range of about 200 yards.see Depth Charges (Patterns) The charges are fired electrically by a ripple switch, firing missiles in pairs, with the highest trajectories being fired first so that all 24 hit the water at about the same time.

The major deficency of the combined SONAR/depth charge attack was the so-called blind times. The first being the time it took a depth charge to reach the depth at which they were set to explode, which increased with the depth of the contact. The second blind time was that at a certain distance, the target would be too close to be spotted on SONAR. A good submariner could use these blind times to avoid the attack.

The Hedgehog was a crude 24-spigot mortar firing about 270 yds or 250 meters ahead of the attacking ship, shortly after blind time began. It fired a circular salvo in the general area of the submarine, each missile or mortar round containing 30 lbs of TNT or 35lbs of Torpex. The missiles were contact fuzed, thus only detonating when actually hitting a submarine.

It is not known of any submarine surviving a hedgehog hit. Hedgehog was only fitted to destroyer escorts and British-build frigates during the war. The difference between the Mk 10 and Mk 11 was that the Mk 10 fired an eliptical pattern, and the Mk 11 a circular pattern.