Martinsyde RG

The Martinsyde RG started its life as a derivation of the Elephant with an experimental single-bay configuration. It was also designed by A.A. Fletcher and it looked kinda like its predecessor, the Elephant. It flew for the first time in late 1916 powered by a 190hp Rolls-Royce Falcon I 12 Cylinder water-cooled engine and it was armed with a single Vickers 0.303in fixed machine gun on the port upper longeron, outside the cabane struts plus a Lewis gun on the starboard of the cockpit.
It was officially tested in February 1917 and then it was revised to correct some aspects. The cockpit was moved aft and the centre section cut-out was enlarged. Lower wing's span was reduced and rear top decking was raised. The armament was replaced by two 0.303in Vickers placed in front of the cockpit, and the engine was replaced by a 275hp Falcon III. That way, the RG had a performance "far and away better than any other machine manufactured", according to the official testing report. However, development was abandoned in favour of the superior Martinsyde F.3.

Source:
1. Salamander Books - The Complete Book of Fighters
2.  British and Allied Aicraft Manufacturers of the First World War.