It's a hurried story of enemy spies sending signals to German U-boats offshore about the sailing of American cargo ships down the coast. Of course it's low budget and rude but I kind of liked it. (The Morse code used is real, not just gibberish. That is, somebody CARED.)
It's 1942 and the US is having a tough time with so many freighters and tankers being sunk off the coast. And they were being sunk in numbers, too. The U-boats called it the second "happy time." But it didn't require Nazi spies. The US had just entered the war and unlike Britain had no clear idea of how to proceed with the business of protecting its shipping. The coast was considered safe from submarines because of the submarine's short cruising range. But they were supplied mid way across the Atlantic by Milchkühe, "milk cows."
The cities along the coast -- Boston, New York, Charleston, and the rest -- left their lights on at night, so U-boats could silhouette our ships easily. It was so easy for the U-boats that the crews sometimes greeted survivors and distributed food to the lifeboats. "Charge this to Churchill."
In this movie, the FBI, realizing that the unnecessary transmitter must be tiny and portable, and must be carefully attended, sees to it that dozens of radio engineers are fired, hoping that one will be approached by the Nazis. Richard Arlen is one of the experts fired and the Nazis offer him a job which, all unwittingly, he accepts.
True. It's as improbable as all hell. Furthermore, these white-collar types lead stuffy lives. They all wear suits and ties, their shoes are shined, and their manners unimpeachable. Dwight Frye ("Renfield") is cast as a Nazi agent. The non-diegetic music is out of a Saturday-afternoon serial, popular at the time. But please, let's not get off on a tangent. Let's stick to events, shall we?
It's a little puzzling that after the FBI's machinations that result in the firing of all these radio experts, those that are offered jobs are treated as potential traitors. After all, they've done nothing but legally exercised their skills. Frankly, I didn't get the logic. But in any case, the lead character, Richard Alrlen, a dull actor, is followed by an FBI agent, Wendy Barrie. He falls in love with her fifteen minutes after they first meet. The evildoers try to steambath Arlen and Barrie to death. It doesn't work.
It's dumb but comforting, like hearing a Kindergarten child recite the ABCs flawlessly and everyone is happy.