An American warship has been damaged after a tug boat drifted into the destroyer during a drill off Japan. The guided-missile destroyer USS Benfold, was in a scheduled towing exercise in Sagami Bay when the Japanese tug lost propulsion. Officials say no one was injured, and the destroyer sustained minimal damage. The US 7th Fleet has been involved in a spate of collisions in Asia this year. Two incidents in June and August killed 17 persons in all. Two more lesser-known incidents left no casualties.