Who achieved the first American victory at Pearl Harbor?

The Ward was on a precautionary patrol off the entrance to Pearl Harbor when, at 03:57, the coastal minesweeper Condor signaled it by visual signals that it had spotted a periscope, and the destroyer began searching for the contact. Around 06:37 it sighted a periscope that appeared to be following the cargo ship Antares and attacked the target. It fired several salvos from its main battery, hit the submarine's turret, and also dropped several depth charges. Although it was not confirmed at the time, its guns had pierced a two-man Japanese Ko-hyoteki class midget submarine.

The PBY's involvement began at 7:00, when a patrolling Catalina found a Japanese midget submarine just outside Pearl Harbor. Together with the destroyer Ward, the PBY dropped its depth charges on the submarine. The flying boat sent a coded message to its base at 7:15, but by the time it was decoded and reached CINCPAC, Japanese bombs were already falling.

The deaths of the midget submarine's two crewmen were the first casualties caused by the Americans in the Pacific theater of World War II, and occurred a few hours before Japanese carrier-based aircraft attacked Pearl Harbor.