(1,360 kg, 3,000 lb blast class), a multi-channel GPS receiver and integration of the buffer box into the GPS receiver. The upgraded avionics package was retrofitted into all existing CALCM (Block 0) so all AGM-86C missiles are electronically identical. Design All variants of the AGM-86 missile are powered by a Williams F107 turbofan jet engine that propels it at sustained subsonic speeds and can be launched from aircraft at both high and low altitudes. The missile deploys its folded wings, tail surfaces and engine inlet after launch. AGM-86B/C/D missiles increase flexibility in target selection. AGM-86B missiles can be air-launched in large numbers by the bomber force. B-52H bombers carry six AGM-86B or AGM-86C missiles on each of two externally mounted pylons and eight internally on a rotary launcher, giving the B-52H a maximum capacity of 20 missiles per aircraft. An enemy force would have to counterattack each of the missiles individually, making defense against them costly and complicated. The enemy's defenses are further hampered by the missiles' small size and low-altitude flight capability, which makes them difficult to detect on radar. AGM-86B The nuclear armed AGM-86B uses a terrain contour-matching guidance system (TERCOM) to fly to its assigned target. AGM-86C/D The AGM-86C/D CALCM carries a conventional high-explosive payload rather than a thermonuclear payload. This is a fragmentation warhead in the AGM-86C and a unitary penetrating warhead in the AGM-86D. The AGM-86C/D uses an onboard Global Positioning System (GPS) coupled with its inertial navigation system (INS) to navigate in flight. This allows the missile to guide itself to the target with pinpoint accuracy. Litton Guidance and Control, and Interstate Electronics Corp. were the guidance contractors for the C model. Operations The CALCM became operational in January 1991 at the onset of Operation Desert Storm. Seven B-52Gs from Barksdale AFB launched 35 missiles at designated launch points in the U.S. Central Command's area of responsibility to attack high-priority targets in Iraq. These "round-robin" missions marked the beginning of the operation's Air Force component and were the longest known aircraft combat sorties in history at the time (more than and 35 hours of flight). CALCM's next employment occurred in September 1996 during Operation Desert Strike. In response to Iraq's continued hostilities against the Kurds in northern Iraq, the Air Force launched 13 CALCMs in a joint attack with the Navy. This mission has put the CALCM program in the spotlight for future modifications.