At the start of the war the US Mark 13 torpedo had to be dropped at 50ft at 110 knots, which resulted in huge losses. By 1944, however, the US had devised plywood devices that were attached to the torpedoes that allowed drops from 800 feet at 300 knots. Combined with improvements to the torpedo itself, the Mark 13 became a very effective weapon.
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Are those additions meant to raise the bouancy, or are they ablative to take the impact and break off?