The GC gearbox, operating below the first lateral critical speed, is especially amenable for internal combustion and steam turbine drivers. This vertically split gearbox features a coaxial gear set arrangement (three side shafts) with the pinion gear centered by tooth forces. The double increasing gear set utilizes roller type bearings on the slow shaft and journal type bearings on the fast shafts. The gearbox may be fitted to air-ends from the KA5 through the KA66.