I had one while trying to iron our some issues with RFB. Had a lone tanker spotted off my starboard bow about 5000 yds away. I moved my boat to get into attack position off the tanker's starboard side and went to periscope depth. Out of nowhere, my sonar man started calling out contacts non-stop. I raised my scope to see a convoy that stretched from the "lone" tanker all the way south out of visual range. I counted 50 tankers, all the same make, all heading north at 9 kts. For giggles I went to third person camera and started heading south with it along the convoy and it never ended. I fired two fish at the first tanker and sank it. Fired two more at the second and they just passed right through it. Literally. Reloaded and fired two more, same deal. Never could work out the issues I had with RFB and, to this day, can't figure out how the tanker got replicated so many times.
Downloaded TMO and haven't had in issue since.