The USS S-51 was trapped in a cave for 24 years - Apparently.
The USS S-51 was a US Navy submarine that was accidentally trapped in a cave in the Florida Keys in 1925. The sub was on a training mission when it became stuck in the cave, and despite numerous attempts to free it, it remained trapped for 24 years. The sub was eventually recovered in 1949, but not before it had become one of the longest-trapped vessels in history. The incident was documented in official Navy records and has been verified by historians.