Amaldo -
John Campbell, in "Naval Weapons of World War Two", indicates the standard British Mk VII depth charge (containing 132 kg explosive, but cast iron weights were attached to increase sinking velocity) could split a 22 mm pressure hull at a distance of 6 meters with early explosives. More brisant explosives available later in the war theoretically increased this distance to 8 meters. The destructive effect of detonation varied with the position of the detonation with respect to the hull (forward, aft, above, below, etc.), but it was estimated that a submarine would be forced to surface if detonation occurred within twice the above distances.

The United States experimented with a magnetic pistol intended to actuate between 6 and 7.5 meters of a submarine hull. This work was probably based on the British estimate, since the standard Mk 3 and Mk 6 US depth charges contained 136 kg explosive. Modern US destroyers also carried larger Mk 4 and Mk 7 depth charges with 272 kg explosive; and the British Mk 10 depth charge fired from a torpedo tube carried 907 kg of explosive. Effective distance would increase as the square root of explosive weight, however, so a pattern of smaller charges might be more effective than a single large charge. =AL=