English: A U.S. Air Force Boeing RC-135M Rivet Card (s/n 62-4132) in flight over South East Asia. The RC-135M was an interim type with more limited electronic intelligence capability than the RC-135C but with extensive additional communications intelligence capability. For most of the Southeas Asia War, unarmed RC-135s maintained a continuous, 24-hour orbit near the border of North Vietnam. They were operated by the 82nd Reconnaissance Squadron during the Vietnam War from Kadena Air Base, Okinawa (Japan), 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 Joint. 62-4132 surpassed the 50,000 flying-hour mark in March 2008.