Congressional Republicans just got their battleship sunk. Even though House conservatives fought in May to prevent the Navy from spending any money on biofuel, the service last Friday launched its "Great Green Fleet"—the first-ever US flotilla to get underway with mostly non-conventional fuel. But election-year jockeying may mean an epic battle over biofuel in Washington this fall. The fleet—technically, an aircraft carrier strike group—is cruising its way to a naval exercise on more than half biofuel, which derives its brew from sustainable biomasses. It's taking place against a major backdrop: The exercise, known as RIMPAC, is a biennial tradition for 22 nations with big-time seapower. It's like a global Boy Scout jamboree for sailors with nuke subs and cruise-missile-laden warships instead of merit badges and pocketknives. "The reason we're doing this is that we simply buy too many fossil fuels from either actually or potentially volatile places on earth," Navy Secretary Ray Mabus said last month. Mabus plans for the Navy to fulfill half of its energy needs using biofuel by 2020.