In 1960, the first group of approximately 50 North Vietnamese airmen were transferred to the PRC to begin transitional training onto the MiG-17. By this time the first detachment of Chinese trained MiG-15 pilots had returned to North Vietnam, and a group of 31 airmen were deployed to the Vietnam People's Air Force (VPAF) base at Son Dong for conversion to the MiG-17. By 1962 the first North Vietnamese pilots had finished their MiG-17 courses in the Soviet Union and the PRC, and returned to their units; to mark the occasion, the Soviets sent as a "gift" 36 MiG-17 fighters and MiG-15UTI trainers to Hanoi in February 1964. These airmen would create North Vietnam's first jet fighter regiment, the 921st. By 1965, another group of MiG pilots had returned from training in Krasnodar, in the USSR, as well as from the PRC. This group would form North Vietnam's second fighter unit, the 923rd Fighter Regiment. While the newly created 923rd FR operated only MiG-17s, and initially these were the only types available to oppose modern American supersonic jets before MiG-21s and MiG-19s were introduced into North Vietnamese service (the 925 FR regiment was formed in 1969, flying MiG-19s).