Designed to be used as a 'bunker-busting' weapon, the 321m was capable of moving itself by being mounted on a mobile vehicle. The carrier vehicle was noted as being slow and uncomfortable to operate due to the large amount of heat generated by the engine which was often directed into the driver's cabin making the inside over ninety eight degrees at times. On the top of the carrier vehicle, a 25mm grenade launcher was mounted to ensure security. However this could easily be switched out for a mass accelerated charge cannon or turret emplacement in around three minutes.
The carrier vehicle moved around sixteen miles an hour and was normally air dropped by a gunship of sufficient weight suport. However despite it's downsides, on the battlefield the 231m was an unstopable dreadnaught as it's powerful 321 milimeter shell could easily destroy most targets that smaller artillery pieces could not.
First made in 2179 CE, the 321m was produced in small numbers between 2179 and 2182 before production stopped. During that time around ninety thousand were made, making a 321m a rare but pleasent sight on the battlefield for most soldiers until it was retired in 2190 CE.