A receiver, modeled after the spade-like lug attachment of a M198 howitzer spade, inserts into the recess on the bottom rear end of the left trail of the howitzer. On this end surface is a square hole for inserting the spade key which secures the receiver to the trail. Attached to the receiver is an interface plate that acts as the union between the receiver and a pair of caster wheels. The interface plate has a keyway, in which the receiver bottom inserts, and also has two built-in handles. Two bolts affix the receiver to the interface plate and thread directly into the receiver body. The interface plate is bolted to dual-pneumatic caster wheels. This combination allows the left trail of the howitzer to be mobile and facilitates the increased mobility of the M198 howitzer.