Yes, the superiority is that great lefteyenine...I hate to agree with Gawain but he is correct. Assuming the American force has sufficient ammunition I think say a division could trump a vastly superior force of WWII germans, the technology is just that superior

Saying that the USMC are the best infantarymen in the world by a mile is somewhat misleading...the royal marines aren't famous for nothing...and there are also quite a lot of marines in the US as opposed to UK