Ronald Reagan?
Is our mystery photo Gerald Ford??
Yep


"Ford received a commission as ensign in the U.S. Naval Reserve on April 13, 1942. On April 20, he reported for active duty to the V-5 instructor school at Annapolis, Maryland. After one month of training, he went to Navy Preflight School in Chapel Hill, North Carolina, where he was one of 83 instructors and taught elementary seamanship, ordnance, gunnery, first aid and military drill. In addition, he coached in all nine sports that were offered, but mostly in swimming, boxing and football. During the one year he was at the Preflight School, he was promoted to Lieutenant Junior Grade on June 2, 1942, and to Lieutenant in March 1943"

And contrary to common belief, Ford was probably the most athletic Commander in Chief to ever occupy the Oval Office.