Safeguarding Military Information was a short propaganda film produced by the Academy of Motion Picture Arts and Sciences in 1942.
The film opens with a dramatic explosion of a ship by two undercover saboteurs and then fades into a written "Thoughtlessness Breeds Sabotage" message.
A man with a radio disguised as a hearing aid is sitting next to him, and he sends the message to his confederates speaking in code with an enemy submarine, which blows up the ship.
Probably the most powerful segment is the last, in which a woman at a grocery store, tells the grocer about her son George taking a train to the West Coast, unaware of the person standing behind her.
The film fades into a newspaper room, and an editor hurriedly ordering a re-write after receiving a telephone call.