This was explained in the article right there:

> it suspected that the plaintext of Nr. 173, SIPVX, might be related to the plaintext of the unbroken MVUEH message

It makes sense that Nr. 172 and Nr. 173 might be related since they were sent at around the same time.

In Nr. 173, "ROSENOW ROSENOW" was also present.

It also makes sense that a longer crib would generally be more effective than a shorter one.

▲ booty 7 hours ago | parent [-]

It was partially explained by the article. It was not stated that ROSENOW was repeated in 173, and it was not obvious from the article text why ROSENOW would ever be repeated. Thus my curiosity.

A sibling commenter explained it - Rosenow is both a municipal name and a district name, so naturally it would be repeated. (Like "New York, New York")

    It also makes sense that a longer crib 
    would generally be more effective than a 
    shorter one.

It would seem to me that the odds of looking for even a single ROSENOW in the decrypted message would be plenty. The odds of a single ROSENOW randomly occurring in incorrectly decrypted output are vanishingly small. So it seems to me that looking for ROSENOW is a safer bet vs. looking for ROSENOW ROSENOW -- a single ROSENOW is a great sign you've got the correct key, whereas looking for ROSENOW ROSENOW seems like it would deliver false negatives (think of all the times we say "New York" rather than "New York, New York")

I'm a novice at crypto though, so, maybe I've got that totally wrong.

	▲	pkulak 5 hours ago \| parent [-]
		The reason a crib is useful is because the enigma can't route a letter back to itself. So, you can slide the crib along the message until no letters line up, and that's possibly where it is. If your crib is "the", that's not terribly useful, because it could exist anywhere. The longer the better. I ONLY know this because https://www.youtube.com/watch?v=JsBZOcqZerk, btw.