I intercepted two ships (2 only) carrying a stack of troops toward my shore. I engaged them and sank them both. I remembered distinctly because they both sank like a submarine doing a crash dive. Upon returning to the strategy map one ship sailed away!

It was one of the two I had sunk, badly damaged but still transporting its dangerous cargo. Fortunately I had enough movement left to follow it and this time, blow it up.

This will need to be patched.