You’ll find that the best approach to the Allies is a slow burn. The Axis start off with way more stuff than you, and the 41 scenario just takes that divide to the extreme. It’s best to stay back and slowly accumulate advantage before making your big push. In most cases, defense is stronger than offense in A&A (i.e. INF attack at 1, but defend at 2, and FTRs attack at 3, but defend at 4), so try to use that to your advantage when possible.
One more note for USA. Rather than go straight for Japan’s jugular, try parking the fleet in the SZ that contains the “Solomon Islands” Territory. It’s a nice territory to camp out in with your fleet, as it:
Puts you within 2-moves of Australia, New Guinea, Borneo, Dutch East Indies, and Philippines, the Pacific territories that are either worth a lot of money, are part of NOs, or both.
Keeps you within 2-moves of West US, your spawn point for new units, so new reinforcements will always be on the way and you always have a safe point to retreat to if Japan is too strong for you.
Keeps you more than 2-moves away from SZ63 (Japan’s spawn point for new units), so Japan will never be able to send a large amount of units your way without first spending a turn moving their units towards you (and thus, giving you a hint that Japan is planning on attacking you).
Just food for thought. Of course, Japan has ways to play around you basing your fleet in the Solomon Islands, but that mini-game of fleet positioning is part of the fun of A&A’s Pacific Theater.