The main reason you could do that is because you took London on G2, so he couldn’t possibly increase his naval force (not to mention he lost a fighter off his carrier). Plus, the US didn’t really put any effort into co-guarding the UK fleet because he is trying to go after Japan first.
You made an excellent choice in this circumstance and it is a good example of what I think the German navy was designed for, but in normal circumstances the costs would have been greater and the benefits less if the US/UK had united in SZ8 and built some navy together (and not lose the capital :lol:)