The modern US Marine Corps arrives in 1941

What if the modern US Marine Corps replaced the USMC of 1941?

With its modern weapons, it would dominate; without them, the advantage would be far smaller.

The result depends on whether the modern Marines bring their weapon systems. With aircraft such as the F-35B, they would have an overwhelming advantage over forces equipped for 1941. Personnel arriving without that equipment would lose much of the advantage assumed by the scenario.