In October 1966, strike force F-105 Thunderchiefs were equipped with QRC-160 radar jamming pods whose effectiveness virtually ended their losses to surface-to-air missiles. As a result, SAM attacks shifted to the Phantoms, which were unprotected because of a shortage of pods. To protect the F-4s, rules of engagement that allowed the MiGCAP to escort the strike force in and out of the target area were revised in December to restrict MiGCAP penetration to the edge of SAM coverage. MiG interceptions increased as a result, primarily by 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.