Military Desegregation in World War II

President Roosevelt signs an executive order desegregating the military in early 1942, citing military necessity. What would the effects of this, both during WW2 and after it? Could we see an earlier Civil Rights movement?

There needs to be some rationale for him to do so. Perhaps military efficiency and streamlining the kind of unnecessary redundancy that segregated units led to in the armed forces might work in theory, but in practice I can't see the WWII USA doing this any at all. The WWII USA was very attached to its overall concept of racism, and the kind of changes required for it to get here require PODs far back enough that nothing guarantees the chain of circumstances leading up to Operation White in the first place.

Extremely unlikely under FDR. Southern Democrats made up a significant part of the New Deal Coalition. There would be a lot of opposition among them. It's not impossible and could be sold as a cost cutting move, but unlikely.

If FDR dies not or cannot run in 1940 and Wilkie or another Republican wins, then it would have better odds. The GOP would have nothing to lose, and could pick up votes in 1942 and 1944 in Northern and Western states where there are some black voters. And not pandering to Southern concerns with duplicate facilities would save a small amount of money.