08/31/2015. Remarks by Johan Visschedijk: "The D.H.15 was essentially a D.H.9A airframe which had been modified to accommodate the 500 hp B.H.P. (Beardmore-Halford-Pullinger) Atlantic twelve-cylinder V-engine. As a modification of a tried and tested type, it may have been designed as an insurance against the failure of the D.H.14.

The Atlantic engine was first made in 1918 by the Galloway Engineering Co., and was produced by combining two ordinary B.H.P. cylinder blocks on a common crankcase. These were of cast iron and, as on the original B.H.P. engine, there was no reduction gear. The new engine was selected for mass production, and 25 had been delivered by October 31, 1918. However, just as the original B.H.P. or Galloway Adriatic had given way to the Siddeley Puma, so was the Galloway Atlantic redesigned to become, in effect, a double Puma, with aluminum cylinder blocks. The redesigned engine was named Siddeley Pacific, and was ordered on a large scale.

The D.H.15 served as a flying test bed for the Galloway Atlantic engine, and made its first flight in 1919. In appearance it differed little from the D.H.9A, for the shape of radiator used with the Atlantic differed only slightly from that of the Liberty engine used in the D.H.9A. The chief distinguishing feature of the D.H.15 lay in its long horizontal exhaust pipes; and the forward center section struts were more nearly vertical in side elevation than were those of the D.H.9A.

Despite its experimental nature, the D.H.15 was given an official name: under the scheme of nomenclature defined in Technical Department Instruction No. 538 it was designated Airco Gazelle. Only two were manufactured and serialed J1936 and J1937."