In this case, a more relevant example from World War II might be the exploitation of flaws in the Enigma machine, namely:

1) the re-use of common phrases in weather reports, and

2) the fact that a letter could not be encoded as itself in the ciphertext, providing a mechanism of contradiction that drastically sped up elimination of possible settings

https://en.wikipedia.org/wiki/Cryptanalysis_of_the_Enigma#Op...

Numberphile gives a nice, succinct explanation https://www.youtube.com/watch?v=V4V2bpZlqx8