I believe that Carter is the last President to serve in WWII..
This came up the other day when the news said President Bush 41 was the last to serve. I looked up Carter's record. He was still in the Naval Academy during the war (graduated in 1946). President Bush 41 was the last to actually see action during the war.
But I really shouldn't quibble. During WWII just about everyone served in some way, whether in battle or in training, entertaining the troops, or as a civilian working in a factory making armaments, supplies and equipment for the war effort, etc.