Are you looking for congressional leaks? Or any leaks?

There was the case of Bonner Fellers, a military attache in Cairo who sent updates of British operations and was ordered to use a diplomatic code that had been cracked by the Germans. Intercepts were in Rommel's hands within 8 hours. Ironically, his criticisms of the British officers caused a minor rift when the British intercepted the German retransmissions.

The way the US used this against the Japanese at Midway was fucking brilliant.

Bless that water heater.