Hahaha! I had a similar incident last night. I was patrolling around the Marshall Islands when my sonarman reported a ship. I did the normal intercept thing, but even at 1000 yds I couldn't see it! The weather was a little rough but I should have seen a ship at that range. I went to the sonar room and, yes I could hear it alright, a slow screw, clear as a bell. So I surfaced, and up on deck I went, but no ship!
In the end I concluded that it might have been an enemy sub who submerged after hearing or seeing me. But I was surprised that if he saw me he didn't take a shot at me.
