The French Rubis-class submarine is the smallest nuclear-powered attack submarine ever built by any major navy — just 240 feet long, displacing 2,700 tons, with a crew of about 70 sailors. It also “sank” two U.S. Navy nuclear-powered aircraft carriers in NATO and U.S. Navy wargames. Once in 1998 against USS Dwight D. Eisenhower. Once in 2015 against USS Theodore Roosevelt. Both times, the French boat slipped inside the carrier strike group’s def…