ARLINGTON, Va. — When the nuclear-powered aircraft carrier USS Nimitz emerged from an extended period in a shipyard last week, it featured a new installation of an anti-torpedo system. Nimitz is the Navy’s fifth carrier to have the Anti-Torpedo-Defense System installed. The system includes the Torpedo Warning System, an acoustic sensor that detects an incoming torpedo; a tactical control station; and the Countermeasure Anti-Torpedo (CAT). The CAT, a small torpedo designed to intercept an incoming torpedo, was developed by Pennsylvania State University’s Applied Research Lab. Compared with air- or ship-launched cruise missiles, anti-ship torpedoes are much more difficult for a...