How plausible it for a German victory in WWII?

[Shaby]

If you know it, then why do you think that Britain could have carried out Gymnast without US involvement?

They certainly were preparing it. If the US is not in the game, then neither is Japan, which gives UK quite a few free divisions and ships. Once more, RN controls the Med. They can send more reinforcements and faster, as well as supply their people in NA and, at the same time, deny this to the Axis.

The invasion of Europe is something else entirely, but anywhere overseas, the British have upper hand...

 

[Realist01]

If as much as half the losses were British (which seems unlikely since the Americans were the majority of the ships and far less careful) that still represents a significant drop in Commonwealth ships lost vs. 1941. If your losses are dropping that seems to show you're winning (or at least shifting the tide).

Even if we assume that you are correct - which I strongly doubt - it would not have mattered that the losses would have been smaller then in 1941 - a loss of 3 million tons in 1942 represents a huge loss to Britain - and may have knocked her out of the war in 1942