In this article they state:
The entire crew of the U-boat is reported to have abandoned ship due to the "monster attack".
Once aboard the British ship HM Drifter Coreopsis, their commander, Captain Krech described their encounter.
He is said to have spoken of a beast with "large eyes, set in a horny sort of skull…with teeth that could be seen glistening in the moonlight".
He apparently claimed that the sub was so damaged in its battle with the "monster", it could no longer submerge.
See Mikes Blog: Lough Foyle Video.
These animals hunt whales close to Stranraer. Lough Foyle Esturary is roughly 100 miles from the where they hunt.