[wat10000]

There was a lot of this. The Enigma cracking team would use things like weather reports and convoy sightings as known plaintext for their work. If you pick up a submarine transmitting near a convoy, it’s probably saying that it saw a convoy at such and such coordinates. The same key was reused for the other messages from that day so cracking one let you read them all.

[WalterBright]

If I was running it and transmitting coordinates, I'd give the U-Boot commanders one-time pads to obfuscate them, and then encrypt the entire message.

> The same key was reused for the other messages from that day so cracking one let you read them all.

I know. The Germans were simply idiots in their hubris about Enigma. The evidence it was cracked was overwhelming, but Doenitz just dismissed it all. Rommel was also defeated by decoded Enigma messages, and he dismissed all evidence of its subversion.

[sidewndr46]

The weird thing is that it's possible the Enigma could have been used during WWII for communications. With the right number of rotors, the right choice of keys, and the right key rotation schedule it is possible.

Of course when you believe you are in the most advanced nation in the US, what is the incentive to improve?

[wat10000]

I wonder how hard it would have been to provision each submarine with enough one-time pad to cover all secure communication for their entire patrol. I don’t know how much radio traffic there was, but it seems like that would not have been a major burden.

[WalterBright]

Hand them a newspaper. Plenty of text there to use as a pad. The code breakers would need to know both the newspaper used, and the algorithm used to select letters from the paper in order to crack it. Or use a magazine to provide the algorithm.

Every U-Boot mission gets another newspaper. Every U-Boot has a different newspaper. There weren't that many U-Boots, so this would be manageable.

Even decoding one U-Boot's transmissions would not compromise the others.

[sidewndr46]

The U-Boats have plenty of other operational failures. Whenever U-Boats would be potentially damaged by the Allies, they'd put a notice in at one of the British listening stations. When the U-boat came into port, it'd radio in advance that it was damaged and might need special provisions (couldn't steer well, etc.) or even a tug to make it into the harbor. This all happened in German on the HF radio, which propagates really well. At least to Britain and possibly all the way to the mainland US.

The Allies basically got free reports of exact damage they inflicted on subs this way. On the other hand if a report didn't show up in a few days, they probably sunk it.