It has always perplexed me how WWII US cryptographers managed to get anything done, when the plaintext still looks like gibberish—further complicated by a novel encoding betweeen a non-western script and EM signals.
I believe the Germans had a policy of starting every message with some standard boilerplate, so Allied cryptographers were usually able to perform known-plaintext attacks with only passive monitoring as long as they observed any one message while it was still unencrypted.
Also the British cryptographers made a practice of “gardening”; before a German expedition was to depart, they’d mine an area so that they’d have known plaintext to work with. I imagine that helped a lot too.
I believe the Germans had a policy of starting every message with some standard boilerplate, so Allied cryptographers were usually able to perform known-plaintext attacks with only passive monitoring as long as they observed any one message while it was still unencrypted.
Also the British cryptographers made a practice of “gardening”; before a German expedition was to depart, they’d mine an area so that they’d have known plaintext to work with. I imagine that helped a lot too.