The improvement in North Vietnam’s air defence system, and particularly the potential of the SA-2 missile, led to the introduction of the RB-66 Destroyer to the conflict.  Two versions of the aircraft were deployed commencing in May 1965.  The RB-66B was originally designed for the night photographic reconnaissance role but a small number of aircraft were fitted with a package of electronic warfare equipment known as Brown Cradle.  These aircraft were limited to jamming the frequencies used by the North Vietnamese air defence radars while the RB-66C not only performed jamming but collected electronic signal information that could be analysed for information on types and location of enemy radars.  The 363rd TRW deployed six RB-66Cs to Takhli in May 1965, followed by three more aircraft in September.  The first RB-66Bs arrived in October 1965 and the 41st TRS was activated at Takhli on the 20th of the month.  The two types were often used in combination during Rolling Thunder strikes with the RB-66C standing off at a distance to locate and identify radars for the RB-66B to move in and jam their transmissions.  The big aircraft were vulnerable to MiG attack and this factor limited their usefulness in that they had to stay out of areas of known MiG activity and often flew with fighter escorts.  In 1966 the aircraft was redesignated as the EB-66 and the EB-66B and EB-66C were later joined by the more capable EB-66E.  With the widespread availability of the QRC-160 self-protection jamming pod from 1967 the role of the EB-66 changed from standoff jamming and ECM escort for USAF strike aircraft to the protection of B-52s and Navy tactical aircraft.