How shallow-water torpedo drops shaped harbour attacks

An aerial torpedo can continue downward after entering the water before its controls bring it to running depth. In a shallow harbour, it can strike the bottom or become buried in mud. Japanese wooden fins improved the drop, while the British system also used a tension wire to control entry. At the intended release height, a Swordfish's torpedo could enter with a shallow belly flop. Dropping too low could instead produce a tail-first entry. The Royal Navy's concern with attacking fleets in harbour encouraged this development after its experience of the German fleet remaining in port during World War I.