Factual error: John Wayne's squadron lands on Guadacanal as part of the "Cactus Air Force" in August 1942. However, they are flying F6F-3 Hellcats, which were not available, even to the Navy, until the middle of 1943. To top it off, they are painted in a late-war camouflage scheme with late-war markings.
Factual error: The postage stamp used on the letter during the scene at the door/porch back home was issued by the post office in Dec. 1949. The stamp didn't exist in 1942.