Around noon on Jan. 4, 1961, after spending hours feeding mounds of government documents into an incinerator, three American Marines assigned to the embassy guard force in Havana turned their attention to a solemn task: lowering the American flag.

As they stepped outside, the Marines were greeted by a throng of Cubans who had gathered. Many of them were clamoring for visas, hoping to get a ticket out before diplomatic relations between Washington and Havana were formally severed.

“We looked at the flagpole, we looked at them, we looked at the flagpole, we looked at them,” James Tracy, one of the Marines, recalled. “I guess they got the idea. They cleared the sidewalk.”

Mr. Tracy saluted the flag as Larry Morris pulled the halyard. Once down, Mike East grabbed the tips of the flag as his two comrades stepped in to help fold it. The Cubans gave them polite applause as the men headed back into the building.