The personnel in several U.S. submarines during World War IT were certain that they were being grappled for by Japanese anti-submarine surface vessels. In some cases, the submariners were equally certain that their submarine bad been caught by a grapnel.
In the case of the CREVALLE, which had been bottomed, she was literally towed a short distance into deeper water – the changing depth on the depth gauge attesting to this. (Remember that a submarine at neutral buoyancy – and that’s the condition for a bottomed submarine -· is just about weightless and can be easily towed by a small ASW warship.)
Submariners weren’t imagining this sort of thing. The Japanese did have an explosive grapnel which was labeled the “Mine Type JD” and was used mainly to destroy snagged enemy mines. But it could have been used against a submarine – the mine exploding against the side of a submarine which bad been grabbed.
The Type JD grapnel-mine, labeled the explosive hook is shown here; reprinted from a Navy Department Bureau of Ordnance pamphlet on Japanese Underwater Ordnance. dated 20 April 1945.In part, the Type JD mine is described: “When used as a grapnel, a sweep wire serves as the towing cable. The mine, with charge of up to 19 lbs of Type 88 granular explosive, has a towing bracket on each end. It is electrically connected to the towing ship by a rubber covered cable. When an object is snared, an observer on the towing boat fires the charge electrically. Or, it fires automatically when an additional tension of 55 lbs is put on the mine.