From the Patrol Report of Lieutenant-Commander Edward Bickford, on HM Submarine Salmon:
Nothing of interest occurred until December 4th, when I was on patrol in my area and at 1330 a U-boat was sighted in position 57° North 5°10′ East by my First Lieutenant. Its conning tower appeared like a box floating in the water, but he had noticed that it did not go ‘up and down’ with the waves and had come to a shallow depth for further investigation. Simultaneously the Asdic office reported a hydrophone effect on the same bearing.
On going to the periscope I found the U-boat to be steering approximately 350 degrees, evidently on passage outward bound. I was a long way off track and closed her at full speed and eventually fired at 5,000 yards on 110 degrees track, the salvo being spread at seven-second intervals, torpedoes being set at eight feet.
At least one torpedo broke surface and much disturbance was visible on the surface on firing. I lost trim temporarily but regained it in time to be at periscope depth before my shot could have taken effect. I saw her through the periscope blown to small fragments which rose at least 200 feet into the air.
I surfaced to pick up survivors but found nothing but oil, wreckage, one dead body and a lifebelt. Bubbles continued to come up from the bottom for some time. Many volunteered to swim out through the oil to retrieve the life belt as a memento. I considered this unnecessary and, fearing aircraft and the possible presence of another U-boat, I dived once clear of the oil patch. The U-boat had one gun and was therefore of the sea-going or ocean-going class. It is impossible to tell the difference between these types except at close range …
The U-boat was U-36, commanded by KrvKpt. Wilhelm Fröhlich on his second patrol.
See TNA ADM199/1839