 Scoring its first kill on October 5, 1966, in December intercepting MiG-21s shot down two F-105s and forced 20% of all strike sorties to jettison their bombloads.The agility of the MiG-21 and the VPAF tactic of high-speed slashing attacks from astern under GCI control posed a challenge to American pilots, who had become predictable by staging large formation strikes from Thailand flying roughly the same routes and times of day allowing the VPAF to challenge them with a relatively small force of 15 or 16 MiG-21 fighters used as point defense interceptors.The USAF pilots were constrained by their rules of engagement and thwarted by a fleeting adversary that only engaged when the situation was ideal.