I have a couple of threads related to this topic. I even started a new campaign with the U.S. to make a small AAR include some battles in the Aleutian Islands and Guadalcanal.
http://forum.shrapnelgames.com/showthread.php?t=48136
I remember in the first campaigns I bought Team Co 42. Then I saw that Sherman was stuck in the ground and tried buying companies of infantry supported by light tanks M3. In the early battles made the difference. It is true that the guns are very important. But more important are the antiaircraft because in the first battles swarms of Japanese planes sent.