Loose Lips Sink ships
Meaning
You must keep this secret or there will be a price paid.
Example
Do not discuss any of our plans outside this boardroom, remember loose lips sink ships.
Origin
Popularized by U.S. military propaganda during World War II. The phrase was meant as a reminder that classified information was never to be discussed with proper clearance and a need to anyone without know.
Specifically, the phrase means that disclosing a military secret to the enemy could result in large loses, such as the sinking of an entire ship.
