Days after Gemini IV hit the waves of the Atlantic, the United States Military Command in South Vietnam announced that its troops would shortly begin fighting alongside South Vietnamese forces against the pro-communist North. It was the beginning of a long, bloody and infamous phase of American history that would see a markedly different United States by the end of the decade compared to that which John Kennedy had inherited in 1961.

Yet Kennedy himself was at least partly to blame for the steady escalation in the conflict in south-east Asia, as was his presidential successor, Lyndon Baines Johnson (LBJ). In fact, one of the issues Kennedy had faced during the I960 election was a perceived ‘missile gap’ between America and the Soviets and in his inaugural address he had promised to ‘‘pay any price, bear any burden, meet any hardship, support any friend, oppose any foe, in order to assure the survival and success of liberty’’. hollowing the crisis of the Bay of Pigs and the erection of the Berlin Wall, however, Kennedy feared that if his administration did nothing to halt the incessant advance of communism from North into South Vietnam, the United States would lose all credibility with its allies.

His initial move was to increase American troop numbers and, although he felt that President Ngo Dinh Diem must ultimately defeat the communist insurgents, the poor organisation, corruption and incompetent leadership of the South Vietnamese military made this an unlikely prospect. A key facet in the effort to isolate the populace from the communists was the Strategic Hamlet Programme, established in 1961, yet even its provisions of improved education and healthcare did little to prevent its infiltration by guerrilla factions. Moreover, the South Vietnamese peasantry resented being uprooted from their ancestral villages. As a result, by 1963, the project had all but collapsed.

That summer, some Washington policymakers were predicting that Diem’s inability to subdue the communists might force him to make a deal with North Vietnamese premier Ho Chi Minh. His main concern seemed to be the need to fend off military coups against himself and, according to Attorney-General Bobby Kennedy, “Diem… was difficult to reason with’’. Early suggestions to encourage a coup and forcibly remove Diem from power were ultimately discarded, for fear of the potential destabilising effects of such an action, and it was decided instead that his younger brother, the hated chief of the secret police, Ngo Dinh Nhu, be removed instead. Only weeks before Kennedy’s assassination, the CIA advised anti-Diem generals that the United States would support his removal from office. On 2 November, during a failed attempt to escape, Diem and Nhu were captured and summarily executed in the back of an armoured personnel carrier.

Kennedy, who had not approved such an act, was visibly shocked and in the wake of his own assassination three weeks later the South Vietnamese situation bounced from one military junta to another, all of which were regarded as nothing more than puppets of the United States. Their existence served only to encourage North Vietnam to consider the leaders of the South as slaves of colonialism. Indeed, in the wake of the Diem and Nhu murders, the number of American ‘military advisors’ multiplied to 16,300 to cope with rising guerrilla violence. Fears that the pro-communist Vietcong retained de facto control of the South Vietnamese countryside prompted the United States to adopt a different policy of pacification and ‘‘winning over hearts and minds’’.

In the aftermath of Kennedy’s assassination, Johnson asserted his own support for continued military operations in South Vietnam, before the end of 1963 pledging $500 million in aid to Saigon. In August of the following year, the destroyer Maddox, on an intelligence mission along the North Vietnamese coastline, fired upon several torpedo boats in the Gulf of Tonkin. Two days later, an alleged attack on the Maddox and another destroyer, the Turner Joy, prompted the Americans to initiate air strikes, marking their first large-scale military involvement in the conflict. Although the second incident was later discovered to be an error, it led Congress to pass the Gulf of Tonkin Resolution, giving Johnson the authority to assist any south-east Asian nation under threat of communist aggression. Over the years, the Gulf of Tonkin ‘error’ has prompted some observers to argue that Johnson deliberately misled the American populace to gain support for greater involvement in Vietnam. Others refute this, but suggest that Robert McNamara and the Pentagon were in the mood to retaliate and presented their ‘evidence’ of the attacks to support their case.

In February 1965, an attack on a Marine barracks in Pleiku led to the ignition of Operations Flaming Dart and Rolling Thunder, a pair of vigorous aerial bombing campaigns to force North Vietnam to terminate its support for the Vietcong. The campaigns would last for three years, depositing, by November 1968, over a billion kilograms of missiles, rockets and bombs into North Vietnam, along the Ho Chi Minh Trail in Laos and Cambodia and onto Vietcong installations in South Vietnam. Ultimately, it failed.

A month after the Pleiku attack, 3,500 Marines were deployed to South Vietnam to help defend the United States’ air bases, effectively beginning the ground war, with public opinion overwhelmingly supporting the move as part of a global conflict against communism. By the end of the year, troop numbers had swelled to 200,000. It was a commitment which many would regret as the Sixties wore on and the death toll rose, with the phrase “Hey, hey, LBJ! How many boys did you kill today?’’ chanted by protesters on the steps of the Pentagon in late 1967.

By the second half of the Sixties, with almost half a million American troops in Vietnam, many of the astronauts were developing itchy feet to return to active military service. “We were uncomfortable wearing the hero image,’’ wrote Gene Cernan, “while our buddies were bleeding, being captured and dying in a real shooting war for which we had been trained.’’ Some of them, indeed, approached Deke Slayton with a view to taking leave of absence from NASA, polishing up their carrier landing qualifications and returning to the front line… only to be awakened to the harsh reality. They were free to leave, if they wished, Slayton told them, but he offered no guarantees of a job when they returned.

“The Pentagon hammered in the final nail,’’ continued Cernan. “We could return to active duty if we wanted to, and even fly, but never – ever – would we be allowed into combat.’’ The negative propaganda impact of the Vietcong capturing American astronauts in a combat zone was too unpalatable for the Johnson administration to bear. “Vietnam,” wrote Cernan, “would not be our war.’’