Last September, American weapons manufacturer United Defense Industries demonstrated a new, cheaper and lighter self-propelled artillery piece to replace the cancelled Crusader system. A month later, they demonstrated the same 20 ton armored chassis with a 120mm gun (same as used on the M-1) in a tank turret (smaller than used in the M-1). The new system was called "Thunderbolt" and included an autoloader and an undisclosed number of rounds carried. The armor can only stop 30mm armor piercing shells in the front, and 14.5mm machine-gun bullets on the sides. Expensive composite armor was used to achieve this much protection. In other words, any tank in the world could knock out Thunderbolt with one shot. But the 120mm gun can also destroy any tank out there (except the M-1, from the front). United Defense Industries was quite proud of the fact that it only took them seven months to put all of this together (although a lot of work was shared with the self-propelled artillery project.) The big question is, if Thunderbolt were ordered into production, how long would that take? A "demonstration model" has not done any of the difficult and time consuming work to insure that the vehicle would stand up to field use. Another potential showstopper is the wear and tear the 120mm gun puts on the lighter (20 ton, versus 60 tons for the M-1) chassis. The stress and vibration problems can require major design changes (either a smaller weapon or a heavier chassis.) Then again, Thunderbolt is taking advantage of the fact that M-1s don't get hit much by large caliber guns in combat. Thunderbolts, being smaller, would probably get hit less. Thunderbolt also uses a novel electrical drive that allows for four hours of "silent operation" (moving just under electrical power.) This could be useful. But in Iraq, M-1s did get many hits (nearly all ineffective) by RPGs. Moreover, because the 120mm gun is a "one shot, one target destroyed" kind of weapon, you wouldn't have to fire many rounds in combat, so the smaller ammo capacity of the Thunderbolt would be less of a problem. But to train the crew, you have to fire that 120mm gun a lot. If you can't train the crew, might as well not take the vehicle into combat. Thus it is unclear exactly what Thunderbolt is trying to demonstrate.