The United States has agreed to spend $23 million to provide new components for many of the several hundred MIM-72 SAMs (surface to air missiles) Taiwan bought from the Americans in the 1980s. These missiles were used on the 90 Chaparral air-defense missile systems Taiwan purchased. Chaparral was basically an M113 armored vehicle with the top and side armor removed and a launcher holding four early model Sidewinder air-to-air missiles in the rear. These Sidewinders were reconfigured for use from the ground and called MIM-72. The U.S. Army bought 600 Chaparral vehicles from 1969 to 1997. Also mounted on the vehicle were an optical sight for the helping to find and aim (in the general direction of) the target aircraft.
The original MIM-72 had a range of 8,000 meters and was still a heat seeking missile. Later versions of the Sidewinder were used and the final version had a range of 10,000 meters and a much more effective heat seeker (able to detect the target from any angle, not just the rear where the hot exhaust was). Chaparral never got much use and was replaced in 1993 by the Avenger. This was a hummer vehicle armed with Stinger surface-to-air missiles, a .12.7mm (50 caliber) machinegun, radar and laser range finder. The hummer has a turret mounted on the back that contains two missile pods (each containing four Stinger anti-aircraft missiles). Under one pod there is an M3P .50 caliber machine gun. The weapons operator has use of a FLIR (night vision) and a laser range finder. The Avenger machine-gun can't be depressed sufficiently to fire at ground targets towards the front of the vehicle. The Stinger has a range of 4.5 kilometers. Effective range of the .50 caliber machine-gun is more like two kilometers.
Taiwan could not afford to replace its Chaparrals with Avengers and preferred the longer range of the MIM-72 missile, especially one upgraded to perform like more modern heat seekers.