Based on a prototype with the factory designation 4A15, the G.I and its successors were built to a conventional bomber design for their time, two-bay biplanes with unstaggered wings of unequal span. The pilot sat in an open cockpit just forward of the wings, and open positions were provided the nose and amidships for a gunner and observer. The engines were mounted pusher-fashion in nacelles atop the lower wings and enclosed in streamlined cowlings. Fixed tricycle undercarriage was fitted, with dual wheels on each unit.
The G.II version was almost identical, but featured more powerful engines and carried a second 7.92 mm (.312 in) machine gun and increased bombload. The G.III was again similar, but had engine nacelles that were now mounted on short struts clear of the lower wing.