The 5th AAF was stationed in the South Pacific.I think that you should be looking in either the 8th or 9th AAF, both of which were stationed in England.
The 8th AAF was the single largest "employer" in the ETO during WW2.You really need to refine your search to a Group or Squadron in order to have any chance of success.
He is buried in South Dakota at the Black Hills National Cemetery.
Loomer, Myron H, b. 03/30/1914, d. 12/17/1975, CPL U S ARMY, Plot: C 711, bur. 12/22/1975,
The office there should have some detail on his unit of assignment.Once you determine the number of the Group, Squadron or attached unit it will be a simple matter to find out where he was stationed.
I also note that Pauline Loomer is buried with him there, and she is listed as a US Army vet as well.I think that you should consult the newspapers where they were married and/or where they lived to get a handle on their unit assignments.