as their primary equipment, while other squadrons used it in small numbers. No. 1 (Fighter) Squadron, a Canadian Air Force unit, formed with Dolphins at RAF Upper Heyford. The unit became operational shortly after the Armistice. In October 1918, the American Expeditionary Force purchased five standard Mk Is for evaluation, sending four back to the United States. The highest-scoring Dolphin unit was No. 87 Squadron, which shot down 89 enemy aircraft. Pilots of No. 79 Squadron shot down 64 enemy aircraft in the eight and a half months that the aircraft was at the front. The top two Dolphin aces served in No. 79 Squadron. Captain Francis W. Gillet, an American, scored 20 victories in the type. Lieutenant Ronald Bannerman, a New Zealander, scored 17 victories. The third-ranking Dolphin ace was Captain Arthur Vigers of No. 87 Squadron, who attained all 14 of his victories in the same aircraft, serial no. C4159. Another notable ace, Major Albert Desbrisay Carter of No. 19 Squadron, obtained approximately 13 of his 29 confirmed victories in the Dolphin. Captain Henry Biziou scored eight victories in the type. Engine problems The scarcity and unreliability of the French-built Hispano-Suiza 8B engine proved to be the most serious problem in the deployment and use of the Dolphin. Use of insufficiently hardened metal in the pinion gears led to numerous failures of the reduction gearing, particularly in engines built by the French firm Brasier. The engine also suffered persistent lubrication problems. Limited production capacity for the geared Hispano-Suiza HS.8B engine and the priority afforded to French aircraft like the SPAD S.XIII slowed Dolphin deliveries. Availability of the Hispano-Suiza improved in early 1918 as the French firm Emile Mayen began deliveries on an order placed by the British Admiralty. Use of the Lewis guns The official armament of the Dolphin was two fixed, synchronized Vickers machine guns and two Lewis guns mounted on the forward cabane crossbar, firing at an upward angle, over the propeller disc. The mounting provided three positions in elevation and some limited sideways movement. The Lewis guns proved unpopular as they were difficult to aim and tended to swing into the pilot's face. Pilots also feared that the gun butts would inflict serious head injuries in the event of a crash. Most pilots discarded the Lewis guns, though a minority retained one or both guns for attacking high altitude reconnaissance aircraft from below. Pilots of