The gun is the primary weapon on the Mounted Combat System, providing Beyond Line-of-Sight (BLOS) capability up to 12 kilometers, 8 kilometers when the vehicle is moving. The 120 mm gun is a lightweight, compact design, weighing over 2,000 lbs less than the gun currently on the Abrams tank. According to officials at Aberdeen, there has been talk of mounting this gun on the Abrams too.

The gun is the only one of its kind in the world -- the bore is made of high-strength steel and wrapped in composite. The crew operates the gun remotely, from inside a vehicle called the XM1202 Mounted Combat System (MCS), one of eight Manned Ground Vehicle (MGV) variants planned for the FCS arsenal. The system will have 27 ready rounds, enormous bullets loaded into a carousel and ready to fire on command.

Here's a rundown of the entire system. Right now, the Army is in a component maturation phase, with the advanced fire inhibit system, ammunition data link, electric gun turret drive and dynamic muzzle reference sensor all preparing for integration onto the gun itself. That process will occur this summer in Shelby, Michigan. The turret structure is the base of the gun, onto which the fire control sub-system, primary weapon assembly and ammunition handling system are loaded. Finally, the turret is plugged into the mission module on top of the tank.

But let's get to the fun stuff. Firing the weapon.

Once we (I traveled to Aberdeen with three other defense journos) got a full brief on how the weapon works, we were escorted into a concrete bunker maybe 25 yards behind the back of the gun. We sat in front of several large screens and waited for the countdown.

BOOM!

That's a simplistic description, but it's fitting. The gun blast shook the building. I've never been in a real tank when it's firing, so I can't imagine being inside a vehicle when that thing goes off, but it was a huge force, even from yards away in a protected bunker. This particular 120 mm gun, however, is far less powerful (in shock to the vehicle occupants) than the one on the Abrams. Not only does it weigh much less, but it's built with a high-efficiency muzzle break and titanium recoil rails (and a 23.5-inch recoil cycle). The muzzle of the gun is capped by a muzzle break or "pepperpot" -- it's like a colander, essentially -- that also helps dissipate the force of the blast.