Would newer fighters and rifles transform America's opening war?

How much would newer rifles, Mustangs, and Hellcats at the start of the war have changed American performance?

Different rifles would change infantry experience more than outcomes, while Mustangs and Hellcats were already arriving by the time American combat expanded in 1942.

Substituting different service rifles would probably not alter the course of major battles, although infantrymen would notice the handling differences. The Mustang and Hellcat were already entering service by 1942. That timing places them close to the point when the United States began fighting at full scale, even though formal entry came in December 1941. A one-year equipment shift does not create a wholly different war.