USS navy 1988, came up port side 25yrds
I Was going to relieve aft watch, when he said to "tell the captain to pull over, we have a cop behind us", as I cleared the super structure I seen that an object was coming up our port side with flashing lights that looked like a cop car, were steaming at a stearage speed as I just left the Helm, the object was under water and was silent it kept pace for just a few seconds and made a sharp port turn like a tracer bullet out to the horizon. as others observed and was reported to the bridge, the speed proved that it wasnt ours.
The qaurter master was ordered not to enclude it in the logg, I know this because we where friends. And on the same deployment our combat central tracked contacts (AIR) that where not explained and also not logged. The lookouts who observed those contacts were councled by ships command and were told to keep quiet and was told it was new helicopters that the navy was testing. but the speed and course changes told another story. These were frequent occurances.