Early in 1960, President Dwight D. Eisenhower authorized the CIA to recruit Cuban exiles living in Miami and train them for an invasion of Cuba. The group that became known as Brigade 2506 was initially 28 members, including 10 former Cuban military officers recruited by Dr. Manuel Artime, head of the Movimiento de Recuperación Revolucionaria (MRR).

After training in secret camps in the Florida Everglades as early as March 1960, the growing brigade moved its base to the Sierra Madre in Guatemala, which boasted a similar climate to Cuba and a friendly government. That September, a brigade member named Carlos Rodriguez Santana was killed in a training accident, and his comrades chose to name the brigade after his serial number: 2506.

On April 15, 1961, eight B-26 bombers took off from Nicaragua and bombed Cuban military aircraft on the ground, hoping to wipe out Castro’s air force before the planned invasion at Playa Girón. Later that day, two other bombers landed in Miami and Key West, Florida, where their pilots claimed to be Cuban defectors that had participated in the air raids.

This drama was supposed to ensure that the attacks appeared to be the work of Cubans only, lending credibility to the U.S. government’s denial of involvement. But reporters noticed the planes’ guns looked as though they had not been fired, and the planes themselves were of a type not typically used in Cuba. The political fallout from this initial bombing raid—which in fact left much of Castro’s air force intact—led President John F. Kennedy to cancel a second planned air strike that might have completed the job.

Officially, no Americans were supposed to be involved in the failed Bay of Pigs Invasion. Unofficially, a top-secret squadron of pilots flew a last-ditch mission authorized by Kennedy on the morning of April 19, to help defend the overwhelmed invaders at Girón. Due to a misunderstanding over time zones, the bombers arrived an hour before planned escort cover arrived from a U.S. Navy aircraft carrier, and were shot down by the Cubans.

For years, the CIA refused to admit the involvement of these U.S. servicemen in the invasion, even though Castro’s government announced it had the body of an American pilot on the day it shot his plane down. After preserving the remains of the pilot, Captain Thomas Willard Ray, for years, Cuba returned his body to his family in 1979. For its part, the CIA waited until the 1990s—and the declassification of many Bay of Pigs-related documents—to admit Ray’s link to the agency and award him its highest honor, the Intelligence Star.

During the months after the failed invasion at Playa Girón, Cuba and the United States began negotiating for the release of hundreds of surviving brigadistas, then being held by Castro’s government.

In May 1961, Castro proposed exchanging the POWs for 500 large tractors; he later upped his request to $28 million in U.S. dollars. Finally, in December 1962, Castro and the American lawyer James B. Donovan agreed to exchange the 1,113 prisoners for $53 million in food and medicine, to be raised through private donations and corporate sponsorships. (At the time, Donovan was fresh off negotiating the complicated exchange of captured American pilot Francis Gary Powers and for the Soviet spy Rudolf Abel, events that were dramatized in Steven Spielberg’s acclaimed 2015 film “Bridge of Spies,” which starred Tom Hanks as Donovan.)

On December 28, President Kennedy received the brigade’s flag in an emotional “welcome back” ceremony at the Orange Bowl in Miami, promising that it “will be returned to this brigade in a free Havana.”

In August 1961, representatives of all American nations convened at Punta del Este in Uruguay for the Inter-American Economic and Social Council. At a cocktail party, the Cuban revolutionary leader Ernesto “Che” Guevara spoke with Richard Goodwin, then an adviser and speechwriter for President Kennedy. As Goodwin recorded in a secret White House memo declassified in the 1990s, the conversation ranged from the possibility of a “modus vivendi,” or interim settlement, between Cuba and the United States, to the U.S. naval base at Guantanamo Bay and the problems facing Castro’s revolutionary government.

Near the end of the conversation, Goodwin wrote, Che “went on to say that he wanted to thank us very much for the invasion—that it had been a great political victory for them—enabled them to consolidate—and transformed them from an aggrieved little country to an equal.”