The mobile version of the Long Tom rifle is slow, bulky and poorly defended, but it remains one of the most powerful long-range weapon systems still surviving from the days of the Star League. Though it lacks speed and grace, it can provide impressive fire support and defense. The Armstrong mobile Long Tom rifle variant is the last remnant of the Star League's main guardian defense system. This powerful and accurate long-range weapon can reduce most small 'Mechs to scrap heaps.
         The mobile Long Tom is actually a series of tracked vehicles working together to move and position the rifle for firing. However, the system can only be transported slowly. Garrisoned worlds in and near key cities usually possess this system.

         The history of the mobile Long Tom is filled with stories of how the system saved entire cities with its awesome firepower. This immense weapon has enough energy to level an oncoming BattleMech.
         The mobile system operates as a train of five tracked transports. The lead transport is the piloting cab as well as the targeting center, with the targeting system placed on top of the cab. This massive gun cannot be fired while being transported. With its twelve tons of armor and twenty tons of ammunition, the vehicle travels at a snail's pace, topping off at 25.6 kilometers per hour and needing frequent refueling. The sheer weight of the unit requires special heavy roads or rail tracks on which to move. A mobile Long Tom rarely travels cross-country, as there is a good chance that it will get stuck. Fifteen crew members are required to fire and drive the Long Tom.
         The Long Tom excels at long-range attacks but is relatively weak at close quarters, and so tanks, infantry and BattleMechs often defend the unit. Though the Long Tom carries four side-mounted machine guns for close defense, these are hardly enough to take on an armed 'Mech. However, the greatest threat to the mobile Long Tom are aerospace fighters. Rifleman 'Mechs, known for air strike support, are frequently stationed with this unit.

         The manufacturing plants on Mars were destroyed during the Amaris Rebellion, but reports suggest that ComStar rebuilt them at some time as spare parts do tend to appear at times. Also, the ComGuards use often-new Long Toms in their ranks, and the Word of Blake did as well until they were destroyed. Many of those fell to other nations during the Word of Blake Jihad, and so they remain in use today.
         The mobile Long Tom is still a relatively uncommon weapon compared to primary combatants such as BattleMechs, and troopers consider it an honor to serve on this cannon's crew. Very few are stripped for parts; most nonfunctioning Long Toms are maintained as is in case the parts needed to repair them are found. If the mobile system is destroyed, the weapon is mounted in a static defense area such as a fortress or city.