In 1964, the United States secretly agreed to supply a few Martin B-57Bs jet tactical bombers to the South Vietnamese Air Force. The United States had initially been reluctant to equip the Vietnamese Air Force with jet aircraft, since this would be a technical violation of the Geneva Accords and might further escalate the war. However, the US had already equipped other friendly nations in the region with jet aircraft, and pressure from the government leadership in Saigon coupled with a need to boost the sagging morale of the South Vietnamese people, led to a change of heart.
The first VNAF B-57 crews began training in secret with 405th aircraft at Clark AB later in 1964. One of the students was none other than Nguyen Cao Ky, the commander of the VNAF and later president of the Republic of Vietnam. As the crews completed their training at Clark, they went to Da Nang Air Base and flew combat missions with the USAF 8th or 13th Bombardment Squadrons, whichever happened to be on station at the time. To gain combat experience, each new crewmember flew with an American pilot or navigator, whichever the case may be. Eventually, the VNAF crew members flew in VNAF-marked B-57s, but their combat missions always remained strictly under USAF operational control.
The VNAF provisional 615th Bombardment Squadron was formed at Da Nang in anticipation of the B-57's assignment, however South Vietnamese Air Force pilots had severe difficulties operating the B-57. Vietnamese crews suddenly began to complain of various illnesses, which grounded many trainees and brought their training to a standstill. In addition, on January 8, 1966 a B-57 was destroyed in a freak ground accident on February 23, 1966 at Da Nang. From this point on there was very little Vietnamese activity in the B-57 program. On April 20, 1967, the VNAF B-57 operation was formally terminated