Secret Command (1944)

Sam Gallagher returns home to Los Angeles as an undercover spy for the Navy, getting a job at the shipyards where his brother, Jeff, is a foreman. Jeff still resents Sam for abandoning the family years ago and fears he may steal away Lea Damaron, his current girlfriend -- who is Sam's old flame. While Sam tries to sniff out Nazi saboteurs in the plant, he grows closer to Jill McGann, the agent tasked with pretending to be his wife.