The U.S. Army has taken four M8 Armored Gun Systems out of storage and assigned them to the 82nd Airborne Division. Often described as an "airborne tank", the M8 project was cancelled in 1996 in order to use the money saved (over a billion dollars) for other uses (like paying for peacekeeping duty). The M8 was a 1980s project, whose purpose was to provide light infantry forces with a tracked vehicle, equipped with a 105mm tank gun, that could be dropped by parachute or delivered via C-130 transport. The M8 has a three man crew and can be fitted with two different sets of add-on armor. The basic M8 weighs 19.3 tons and has armor that will protect the crew from shell fragments and some bullets. Three tons of additional armor will provide protection from all bullets and some small caliber cannon shells. Add another 2.5 tons of armor (creating a 24.8 ton vehicle) provides protection cannon shells up to 30mm. The M8 looks like a tank, but it isn't. It's best armor protection will not stop the least capable anti-tank round currently in use. The M8 is more like the World War II ear American "tank destroyers," which proved more useful as infantry support vehicles. The Germans and Russians  had many similar vehicles which were accurately described as "assault guns." The M8 has an autoloader with 21 rounds, plus another nine rounds for reloading the autoloader. In practice, the M8 usually functions as self-propelled artillery system for light infantry. Missiles and air power are more likely to be used against enemy tanks and armored vehicles. 

If the M8 had gone into mass production, each one  bought would have cost about five million dollars. The army says it does not plan to resume development of the M8, it just needs some mobile artillery for the 82nd Airborne Division and the M8s were available. Cancelled weapons systems usually have working prototypes into storage in case the project is revived or, in this case, the weapon is actually needed. The new chief-of-staff of the army is said to be in favor of the M8, so putting the four prototypes to use might create enough positive feedback from the battlefield to get the M8 back in the procurement budget. The army originally wanted to buy 237 of them. The 25 ton version would be well protected against RPGs and would provide the kind of direct fire artillery support light infantry find very useful. At the moment, only tanks can provide this kind of support. But the 25 ton M8 can be flown to distant battlefields much more easily than the 65 ton M-1 tank. Development on the M8 has not stopped completely, there's now a version that carries a 155mm howitzer, whose development was paid for by the manufacturer, not the government.