Hi Dave,
The May 4th 1945 attack is difficult to make certain research about, due to the lack of German sources.
The Senja was located near the Black Watch, and is shown covered in swells from exploding bombs on some photographs taken from the aircraft. The Senja (1938/858) was as far as I know still flying the Norwegian flag, and manned by a Norwegian crew. (the Black Watch had a Norwegian crew until 18.3.1943!). The Senja sank in quite deep waters, but was raised in April 1947, and taken to Oslo for repairs (arrived Oslo April 30 1947). Returned into service one year later, and met her final fate May 10th 1973, when she was lost as Greek “Pramnos”. Her loss report is not located in the Norwegian war risk insurance files (if someone have it, please send me a mail). Her damages can’t have been to heavy, as she was lifted from deep waters. The shallower wreck of the Black Watch was just partly broken up “in-situ”.
The motor barge “M.W.6” (1929/163) was a Speerflotte vessel. Previous European river barges (Binnenschiffe) were send to Norway with the Nord Reederei and the Speerflotte in large numbers. River vessels were not very useful at the Norwegian coast, and they suffered a lot from accidents due to bad weather. M.W. = Motor Wiking. She was the ex civilian German vessel “Ruhr” (Kriegsmarine number: C 138 PM). Taken over by Speerflotte 4.7.1942 in Rotterdam, and became “M.W.6”. She probably had a Dutch crew, and was based in Narvik as a supply vessel. Speerflotte just state “lost Harstad by war causes – total loss 5.5.45”, but she was quite certain in or near Kilbotn. She was raised too, and returned into service as Norwegian “Basse”. The Basse sank in May 1949 in Oslo harbour and was lost.
I am sure Theo has much more information about the M.W.6!
The tug is unknown to me (due to the lack of sources), but it would be strange if there weren’t tugs in the area to support the U-boat base, nets, etc

Best regards from the not so warm Norway -15°C this morning in Oslo
Erling