A land-based derivative of the U.S. Navy's E-3 Skywarrior, the U.S. Air Force EB-66, like its prececessor, was an electronic intelligence and electronic warfare aircraft built on a bomber airframe. Neither the basic B-66 nor A-3 were successful bombers, but had long careers in support missions. 
In air operations against North Vietnam, the EB-66C was an electronic intelligence platform capable, over North Vietnam, of identifying FAN SONG ground radars used with the S-75 Dvina surface-to-air missile, as well as MiG fighter IFF (identification friend or foe). The EB-66B/E versions were electronic attack versions used to jam enemy electronics with greater power than could the EB-66B and EB-66E aircraft were used primarily for active ECM using high power barrage and tuneable electronic jamming of selected frequencies.
With the 1967 advent of the F-105 AN/QRC-160 self-protection jammer on the F-105 fighter bomber used in Operation ROLLING THUNDER, the EB-66 specialized in "early warning and ground controlled intercept radars. Flights of three aircraft were used and commonly composed of two EB-66Bs and one EB-66C. Up to three of these flights were used to cover a strike mission during target ingress and egress as well as during the actual strike. The EB-66 could not survive within the lethal SAM envelopes at the altitudes required for area jamming;" they flew just outside the strike area. They also escorted B-52 bombers in Operation LINEBACKER II.