The other day I was looking through a collection of American WWII propaganda posters, and I was struck by the large proportion urging people to secrecy about shipping, troop movements, and the like.
To what degree was this fear justified? Was there any attack that could be traced back to somebody not keeping their mouth shut?
Not to discourage answers, but that question has already been asked
Not to discourage /u/jiandaren1 from linking to earlier iterations of this question, but that thread missed out on one salient point:
The greater effect, IMO, of the "Loose Lips Sink Ships" campaign was keeping civilians from discussing the great successes the u-boats were having.
tl;dr It was more of a PsyOps than an OpSec campaign.
I'll try to find citation for that when I'm back with my u-boat books.