U.S. Army infantry divisions and armored cavalry regiments are equipped with mobile anti-aircraft vehicles called Avengers. They have not got any use in Iraq until recently, until eight of them were recently converted to operate as gun trucks. 

The Avengers are hummers with a turret mounted on the back. The turret contains two missile pods (each containing four Stringer anti-aircraft missiles). Under one pod there is an M3P .50 caliber machine gun. The weapons operator has use of a FLIR (night vision device) and a laser range finder. The machine-gun, however, cant fire, at ground targets, towards the front of the vehicle. 

The 3rd Cavalry Regiment has eight Avengers, and they persuaded the army to send six engineers to Kuwait, where the regiment was preparing to move into Iraq, to modify the Avengers for use as gun trucks. In two days, the engineers removed the right missile pod, and moved the machine-gun up to where the pod was. Some changes were made in the fire control software. All this allowed the machine-gun to fire in any direction, at any elevation. The ammo capacity of the machine-gun was also increased from 250 rounds to 600 rounds. The missiles were removed from the other pod. The two man crew of the Avenger was now ready to use their FLIR and laser range finder to provide accurate long range .50 caliber machine-gun fire day or night. The Avengers were expected to be particularly useful at night.

Converting anti-aircraft guns into deadly ground warfare weapons is nothing new. During World War II, the German 88mm anti-aircraft gun became a very effective anti-tank gun early in the war. Later on, the American anti-aircraft halftrack, mounting quad .50 caliber machine-guns (the famous "Duster"), became much more useful for ground combat, and continued in service into the 1960s (in different forms). Any light, self-propelled anti-aircraft gun system has the potential to become a weapon useful against ground targets. There was a lot of grumbling in the U.S. Army when the M163 (a six barrel 20mm cannon, with over 1,000 rounds in an APC) was retired in the early 1990s. However, many current systems include short-range anti-aircraft missiles, and often are put together so that the gun barrels cannot be depressed enough to hit targets on the ground.