The Navy is replacing dolphins with knifefish: The military use of sea mammals reached its height during the Cold War. It is a story filled with fascination and intrigue, including trained killer dolphins — and even counter-killer-dolphin dolphins. Our enlightened times now herald greater thoughtfulness towards our fellow sapients. New undersea robots like the US Navy’s Knifefish, together with a heavy dose of fiscal reality, have begun to close this chapter of military history. Ah, so the fish is a type of drone. . .