In theory this should be impossible, simply because (1) with the UK building the right ships, you’d eventually lose so many planes you couldn’t keep attacking, but more importantly (2) if nothing else, the UK could simply build a bunch of infantry. Even if Germany has a production of 42 (and if they’re not aggressive against Russia or at least taking back lost territories, they definitely should not have this) and the UK is as low as 18 (again, unrealistic) the UK would still be able to defend itself. They could build 6 infantry in a turn with 18 IPCs. Germany would not be able to use planes they had lost, and after several turns of attacking carriers and possibly American fighters they most likely have lost the majority unless they stopped hitting UK’s fleet. So they’d be attacking only with infantry and/or armor they could transport - even assuming that the UK didn’t have a fleet that turn to destroy first somehow - the UK would still be building 6 infantry per turn directly on London, while Germany would have to spend 14 IPCs for a transport and 2 infantry to transport them with. Even if you use some of the infantry you start with - an asinine idea in my opinion since it begs of Russia “Take me!” - you’re still only getting the ability to go with 6 infantry a turn (3 transports and 6 men = 42 IPCs) or, even worse, substituting a tank (one unit instead of 2) for 2 men, something I think should never be done in a direct amphibious assault on a one-territory island. 6 offensive men should never match up against 6 on defense, and that’s not even including the fact that the UK will be at least 2 turns’ building ahead of you, since to move transports from Italy to UK will take 2 turns. So in theory, you’re facing a minimum 12-men disadvantage with a lower firing rate, less hits for you to get killed, and the fact that Russia will take your capital without any difficulty should you actually play this idea.
As for hitting the US with Germany before Russia, you’d better hope Japan has heavy bombers, long range aircraft, a laughable number of bombers, transports and men just outside WUSA, and the US player is the dumbest you have ever met. The only times I ever took the US with Germany were against that dopey AI and against a kid with ADD, and only against the AI (not even the kid with ADD) have I ever claimed UK before Russia.