To correct one post well up the thread:

The Reuben James was a US destroyer sunk by a U-boat whilst escorting a Uk-bound convoy out of Canada, in the period before the US entered the war but whilst it was escorting convoys partway. I'm sorry I can't recall the hand-over point. I believe that the sinking became quite a cause celebre at the time, the song was written and sung by Woody Guthrie. Nothing to do with the Russian convoys, I'm afraid.