I put my hands up, it wasn’t U109. I would like to thank both Dale and Marozi for pointing this out. I had thought it was just my inability to read numbers that had led to me using the wrong details, however I lay the blame at the door of Mr Heuvelmans' proofreader, I actually took the number from the narrative description on page 400 where it clearly states U109. Every other mention in In the Wake of the Sea-Serpents the submarine is clearly given as U108 which indeed did survive the war.
Before I skulk off embarrassed and a little red faced can I ask if anyone has any more information on this sighting? If so I would very much like to hear from them, going from the location given for the sighting it will now find its way into my next book The Mystery Animals of the Northern Isles which should see the light of day in 2010
all the best for the new year