AGM-22 missile. Sources claim that the XM11 provided an XM70 sight and support racks for 6 missiles, three on each side of the aircraft. However, US Army FM 1-40 says that the XM11 designation was unassigned. The M22 was an improvement providing a more specific sight, the XM58, and using the XM156 universal mount. The M22 also provided for a total of 6 missiles, three on each side of the aircraft. It is important to note as well that the XM11 is associated with the standard SS.11 missiles (AGM-22A), while the XM22/M22 system was designed around the US upgraded AGM-22B missiles. The Maxwell System was a hybrid system designed by Warrant Officer Robert Maxwell as a field modification. Maxwell's unit had been sent both the M3 and XM11 systems, and he noticed that often aircraft with the M3 system returned after only firing half or less than half of their total rocket load. By removing one or two banks of rockets (and reducing the total carried to 12 or 18 total rockets versus 24) and adding a single launching mount for an AGM-22 missile he effectively gave the aircraft both suppression and point attack capabilities. The general lack of point targets in South East Asia meant that SS.11/AGM-22 missile saw very limited use in general. XM16/M16 The XM16/M16 system mated the previous M6 with either two M157 or two M158 2.75" 7-Tube rocket launchers utilizing the M156 Universal Mount. Sighting was accomplished by using the M60 series reflex sight. The combined weight and aircraft limitations meant that only seven-tube launchers could be used. XM17 The XM17 utilized "Kellet pylons" to mount two XM159 2.75" rocket launchers, one on each side of the aircraft. XM21/M21 A further variation on what had essentially become a basic system, the XM21/M21 subsystem replaced the XM16/M16's four M60Cs with two M134 7.62×51mm Miniguns. XM23/M23 The M23 system provides a pintle mount at both main cabin doors for an M60D 7.62×51mm machine gun, with the weapon feeding from either a standard ammunition box or a larger purpose built box connected to the mount. The M23 is specifically designed for long fuselage UH-1s (UH-1D/H/N). XM26 With the development of the BGM-71 TOW missile Hughes had been given the contract to develop a launching system for the UH-1. By 1968 development had shifted over to development of a system for the AH-56 helicopter which was eventually canceled. The