system. Originally delivered as a C-135B, 62-4137 operated from Shemya Air Force Station, Alaska from 1966 to 1969. Its operations were performed in concert with the RC-135S Rivet Ball aircraft (see below). The radar system alone weighed over 35,000 pounds and cost over US$35 million (1960 dollars), making Rivet Amber both the heaviest C-135-derivative aircraft flying and the most expensive Air Force aircraft for its time. This prevented the forward and aft crew areas from having direct contact after boarding the aircraft. The system could track an object the size of a soccer ball from a distance of , and its mission was to monitor Soviet ballistic missile testing in the reentry phase. The power requirement for the phased array radar was enormous, necessitating an additional power supply. This took the form of a podded Lycoming T55-L5 turboshaft engine in a pod under the left inboard wing section, driving a 350 kVA generator dedicated to powering mission equipment. On the opposite wing in the same location was a podded heat exchanger to permit cooling of the massive electronic components on board the aircraft. This configuration has led to the mistaken impression that the aircraft had six engines. On June 5, 1969, Rivet Amber was lost at sea on a ferry flight from Shemya to Eielson AFB for maintenance, and no trace of the aircraft or its crew was ever found. RC-135M Rivet Card The RC-135M was an interim type with more limited ELINT capability than the RC-135C but with extensive additional COMINT capability. They were converted from Military Airlift Command C-135B transports, and operated by the 82d Reconnaissance Squadron during the Vietnam War from Kadena AB, gathering signals intelligence over the Gulf of Tonkin and Laos with the program name Combat Apple (originally Burning Candy). There were six RC-135M aircraft, 62–4131, 62–4132, 62–4134, 62–4135, 62–4138 and 62–4139, all of which were later modified to and continue in active service as RC-135W Rivet Joints by the early 1980s. RC-135S Nancy Rae / Wanda Belle / Rivet Ball Rivet Ball was the predecessor program to Cobra Ball and was initiated with a single RC-135S (serial 59–1491, formerly a JKC-135A) on December 31, 1961. The aircraft first operated under the Nancy Rae project as an asset of Air Force Systems Command and later as an RC-135S reconnaissance platform with Strategic Air Command under project Wanda Belle. The name Rivet Ball was assigned in