At a Naval inquiry, gunner Mike Mallory testifies that Lt. Tom Sands was responsible for an explosion on their ship due to negligence. Tom leaves the Navy and his girlfriend, Myra who is Mike's sister. Tom reenlists when Pearl Harbor is bombed. He joins Mike's crew, a group of gunners aboard a merchant marine ship. When the crew captures a Nazi ship, Mike has a chance to clear his name and reunite with Myra.