A US congressman got 10 submarines sunk and ~800 sailors killed by telling newspapers that Japanese destroyers weren't setting their depth charges deep enough. Source

One things that you also should understand is that intelligence work isn't about someone saying that "X operation consisting of Y men is to take place on Z date at A location". It's about getting small pieces of information, like increased road traffic to and from a particular base (indicating preparations of some sort), and putting that together with other fragments of information. Just telling someone that you're going to X place can give the information of what a side thinks is valuable, and how much they're investing into that area. OPSEC is taken very seriously.

"Loose Lips Sink Ships" was more about military to civilian or unguarded military to military communication: specifically deployed sailors communicating with friends and family back home. There is a very long history of this sort of intelligence gathering and it is currently known as OPSEC (OPerations SECurity).

As this NSA paper states:

Operations Security (OPSEC) as a concept is probably as old as war itself. Nevertheless, the fact that poor OPSEC practices have been costly in loss of human life and lost objectives in every American war demonstrates that, despite its venerated age, Operations Security as a doctrine needs to be learned afresh by each generation.

The attached PDF also discusses "Charlie" use of weak OPSEC to anticipate US forces during the Vietnam war.