I was up there close to Murmansk (raided the harbor first).
Summer '44...when leaving the harbor, I found a huge US convoy, complete with escort-carrier! Most cargos were medium to large.

I guess these convoys will be on a regular base, in that period.
Murmansk is poorly guided...maybe a tugboat, or an armed trawler.
You may sink a few DD's, and some medium merchants in the harbor.
Btw, prepare for only a few meters underneath, when going for Murmansk!
It's around 20m, all the way to the harbor itself.
All this was in a typeXXI career.