Great post Black Elk. Here are my usual US buys for the first 3 rounds.
1st 3 bombers. Save 6
2nd 3 bombers, Transport, infantry
3rd 2 bombers, Transport, 2 infantry
4th turn on can change based on bomber losses, German plane buys, and what Japan is doing.
The point with this build is to merge allied fleets off sea zone 13 on turn 3.