After high school, Carter enrolled at Georgia Southwestern College, in Americus. He would later apply to the U.S. Naval Academy and, after taking additional mathematics courses at Georgia Tech, he was admitted in 1943. Carter performed well at the academy, and graduated 59th out of 820 midshipmen.
Carter served on surface ships and on diesel-electric submarines in the Atlantic and Pacific fleets. As a junior officer, he completed qualification for command of a diesel-electric submarine. He applied for the U.S. Navy's fledgling nuclear submarine program run by then Captain Hyman G. Rickover. Rickover's demands on his men and machines were legendary, and Carter later said that, next to his parents, Rickover had the greatest influence on him.
Carter has said that he loved the Navy, and had planned to make it his career. His ultimate goal was to become Chief of Naval Operations. Carter felt the best route for promotion was with submarine duty since he felt that nuclear power would be increasingly used in submarines. During service on the diesel-electric submarine USS Pomfret, Carter was almost washed overboard. After six years of military service, Carter trained for the position of engineering officer in submarine USS Seawolf, then under construction. Carter completed a non-credit introductory course in nuclear reactor power at Union College starting in March 1953. This followed Carter's first-hand experience as part of a group of American and Canadian servicemen who took part in cleaning up after a nuclear meltdown at Canada's Chalk River Laboratories reactor.
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Upon the death of his father, James Earl Carter, Sr., in July 1953, however, Lieutenant Carter immediately resigned his commission, and he was discharged from the Navy on October 9, 1953. This cut short his nuclear powerplant operator training, and he was never able to serve on a nuclear submarine, since the first boat of that fleet, the USS Nautilus, was launched on January 17, 1955, over a year after his discharge from the Navy.