 Rules of engagement that had previously permitted the F-4 MiGCAP to escort the F-105s in and out of the target area had been revised in December to limit MiGCAP penetration to the edge of SAM coverage.MiG interceptions had consequently increased, primarily due to MiG-21s using high-speed hit-and-run tactics against bomb-laden F-105 formations, and although only two bombers had been lost, the threat to the force was perceived as serious.Bombing of North Vietnamese airfields was still forbidden at the start of 1967, and 8th TFW wing commander Col. Robin Olds proposed an aerial ambush as the best means of mitigating the threat.