After the successful field tests of the RGM-122C it was decided by the Earth Federation to upgrade the remainder of it's failing RGM-119 Jamesgun units into cannon types. Using a series of borrowed thrusters and verniers from the RGM-122 line the Jamesgun was given an additional eight rocket thrusters to replace the loss of power sustained from the replacing of the three original main rockets with three less powerful 21,000 kg thrusters. In addition to the new rocket thrusters the James gun was given addition sensors mounted on either side of the head to compensate for the obscured view thanks to the new shoulder mounted guns, and to give additional accuracy at long range.
During the testing phase for the RGM-119C the two test units came under fire from a BESPA unit patrolling the area around Side 2. The result was the lose of the first RGM-119C Test Unit 1, however, it did well to highlight the added potential of the new modifications of the Jamesgun series. Despite this fact, with The Test Unit 2 also heavily damaged the production line was canceled in favor of newer designs being placed into development. The remaining RGM-119C units were never rolled out, and were subsequently scrapped for parts.