Get a medic truck, any gun that needs two soldiers, a tank, two officers/snipers, and a supply truck. Have the two officers/snipers operate the gun, then order a tank. Fire just one shot at the gun, then immediately press C. After supplying truck fixes the gun, use the medic truck to take the gun. After that, take the gun off. There should be one more officer/sniper. Repeat as much as needed, but the game may crash if done too many times.