Besides, he said, he never received Dewey’s letter asking him to pay up.

In November 1964, Horne tore the cartilage in his left knee during freshman football practice — he never made it beyond the junior varsity — and spent weeks in the hospital. As a result, he watched that year’s Army-Navy game on TV. The rest of the school year was a blur. Back home for Christmas. On campus for final exams. Back in the hospital for surgery. Away in California for summer military training.

Image Greg Horne as a Navy midshipman.

The Army-Navy game was the least of his worries.

A white poster board appeared in the rotunda of his dormitory during Horne’s second year there. It listed several names of Naval Academy graduates who had been killed in Vietnam. The poster would soon be filled with more names, he said. Then another poster would appear, and that one would fill up, too. And then another.

Two years after graduation, at the same time Dewey was in Vietnam, Horne was on a ship off the Vietnamese coast, firing rockets in support of ground troops. He was a weapons and deck department officer in charge of 70 seamen on the U.S.S. White River.

“We trained to be leaders, and that’s what we had to do, whatever academy you came from,” he said. “In the end, and this is important here, we were all in it together.”

Horne was in a battle zone for about three months before being reassigned. By the time he retired from the Navy, he had reached the rank of captain.

He has had season tickets to Navy football for 35 years, but the Army-Navy rivalry never felt as poignant as it does this year — all because of a letter found in his parents’ house after his mother died.