The largest self-propelled gun ever built in the known universe is a Machina (Fondera clan) weapon known as the "Behemoth". The Behemoth looks like a huge cannon mounted between two Elephant (the vehicle)-sized sets of tracks, with a crane behind the gun for lifting shells into the breach. The vehicle has a total length of 100 meters. The gun itself is a 1200mm light MAC capable of pounding both ground and space targets. Even at the lower power settings for attacking ground targets, it's impact created a blast equal to that of an ENTROPY massive fuel-air bomb.
It was built by a group of several Fondera-clan workshops in a manner similar to the construction of a Machina warship. Though the Behemoth proved itself a force to be reckoned with, pounding Remnant and Necros fortifications into dust and providing ground based anti-spacecraft defense of the planet of Kastellia, it was rarely used due to it's size and immobility. It was also horribly weak against aircraft, being a large target with a maximum speed of under two kilometers per hour. The Behemoth was destroyed during the failed Necros assault on Kastellia, when it was bombed by Necros Bombers and Carrion Gunships. In the end, the Behemoth was considered to have been little more than a morale booster and terror weapon, and most military scholars believe that, like 20th century human attempts at constructing superguns, such as the German 800mm Gustav of WWII and the Iraqi 1000mm Babylon of the 1980s, the resources and money used in the Behemoth would probably have been better used elsewhere.