De Havilland DH.15 Gazelle

The de Havilland DH.15 Gazelle, more often called just the DH.15, was a one-off engine testbed for the Galloway Atlantic engine, converted from a standard DH.9A complete with its original armament for flight trials in 1919 and 1920. The engine was a 500 hp water-cooled V-12 produced by the Galloway Engineering Company, formed by merging two six-cylinder inline Galloway Adriatic engines onto a common crankcase. It replaced the 400 hp Liberty 12 of the DH.9A without much change in appearance, because the Atlantic sat behind a similar large rectangular radiator, although the exhaust pipes were longer and ran straight back from the upper sides of the engine to the observer's cockpit. Two DH.15s were ordered but only one was built, and it completed many flights with the Atlantic engine between 1919 and 1920.