About a day out of Cape Town, heading north, I spotted a submarine in the distance, informed the OOW and asked if I could dip to it. He said yes, so I ran up the ensign and watched the sub. Heads disappeared from the conning tower then re appeared and they ran their ensign up. We duly dipped. Their ensign came down as did ours, and we went on our merry way. Quite funny as it appeared that we caught them on the hop.
Another time we were in some N German port when a line of several NATO warships sailed past us. All pretty small stuff, mine sweeper sort of size. I dipped to them, but got a rollocking for not dipping to the last one. I pointed out that that one was under tow and flying no ensigns. Looked like she was not part of the flotilla and looked as though it was more likely to be going to the breakers. "Right" was the Old Mans short reply. Always good for a giggle in the mess later on, that sort of thing.