I was near a port (Whatever that one on the north coast of the Philippines is), nice shallow water. My hydrophone operator started going crazy, calling out "Warship, Bearing <X>! Closing!" over and over again.

I used the external camera to take a look, and there was a task force of cruisers with a whole pack of destroyers, heading right for me. Any wayI headed to get out would take me through the shallows, past the destroyers.
"What the hell", I thought, "I'll at least take out a cruiser before they get me!"

I waited for the right moment to strike, watching those sonar lines creep closer and closer. I came up to periscope depth, raised the scope, and sighted on an empty ocean.
It was kind of a letdown after preparing for the final battle.