Unidentified Submersible Object: the underwater equivalent of a
UFO.
Since WWII, these objects have been showing up both visually and on radar in increasing numbers - although still without anything like the frequency of traditional UFO sightings. They vary in appearance, from brilliant submerged discs to simpler cigar-shaped 'phantom submarines.'
They first appeared in any great number in Swedish waters, and until the collapse of the USSR were believed to have originated in Warsaw Pact countries. This has always been denied, and despite the use of hundreds of depth charges none have ever surfaced.
The following second-hand recount was found on a UFO newsgroup:
"Several years ago we were sailing around the bottom of
Tasmania, near Port Davey, and we know the area can produce good
shows of phosphorescent algae but we weren't prepared for what
we came upon.
I was standing watch aft and it was a beautifully clear night. I
became aware that there very bright submerged lights way ahead
and we were sailing straght for them. As we got closer I could
see how intense they were but I couldn't guage their depth. The
whole area was covered with them and they stretched on into the
distance. I have seen a lot of things at sea but nothing like
this. They looked just like bright light streaming from port
holes in a submarine. (The speaker was a navy diving instructor
for several years.) Also, they were lined up very regularly in
rows - vast rows.
This spooked me like you wouldn't believe so I went and got the
boat owner and showed him. He was awe struck! I told him that I
didn't want to go any further as I feared hitting one or more
solid submerged objects and insisted that we change course. He
agreed and we left the area. I haven't seen anything like it
since and I visit the area on a regular basis in my own vessel
still."