Ground ordnance is a military term.
Ground Ordnance Maintenance is a career field available to members of the United States Marine Corps. Marines in this field are responsible for the maintenance of the weapons and weapons systems used by the Corps.
Marines in the Ground Ordnance Maintenance field are trained in the care of the various weapons systems of the Marine Corps. It is their responsibility to inspect said weapons for potential defects and repair any damage found.
Like all career fields available to members of the military, Ground Ordnance Marines go through training specific to their field. This includes basic recruit training and a technical course on ordnance repair.
There are several specialties available within the larger field of Ground Ordnance Maintenance. These specialties include ammunition technician, small arms technician and EOD technician. The first deals with the care of ammunition, the second with the care of small arms and the third with the location and disposal of bombs and other explosives.