The U.S. was the only participant in World War II to almost completely equip its infantry with automatic weapons. Many U.S. units were formed on a volunteer basis, and all were quite mobile: almost every platoon was equipped with a transport.
They were well stocked with the latest combat gear and weapons, and provided with everything one might need in the pursuit of war. From June to December of 1941, the total number of U.S. forces increased significantly, and by the end of the year their numbers had reached almost 1.4 million troops.
However, in the early days of the war they lacked more sophisticated weapons, including mortars and heavier artillery.