The first of two prototype R.E.8s (Reconnaissance Experimental 8) flew on 17 June 1916. The new type was designed to overcome the failings of the B.E.2 - it had a more powerful motor giving an improved performance, in particular a heavier payload. It was also much better armed, with a synchronised forward-firing .303-in Vickers machine gun and one or two Lewis guns on a Scarff ring in the observer's cockpit, which was finally moved to a position behind the pilot. It was (intentionally) less stable than the B.E.2, although modifications had to be made to improve stability before it could gain acceptance by pilots used to the B.E.2e - making the production version ideal for artillery spotting but giving it little chance of out-manoeuvring enemy fighters. Most R.E.8s were powered by the 150 hp (112 kW) Royal Aircraft Factory 4a air-cooled 12-cylinder inline engine, though some received the 200 hp (149 kW) RAF 4d engine and others had an Hispano-Suiza engine. A shortage of Hispano-Suiza engines and Rolls-Royce aero engines, such as the Falcon, resulted in the RAF 4 remaining the standard engine. It was installed so that the propeller inclined upwards to improve the takeoff and landing run. This produced a "broken back" appearance to the fuselage and an illusion that the tail sloped upwards. Like most RAF engine installations, the twin exhausts protruded over the upper wing to carry the fumes clear of the crew. As with the B.E.2e, the long extensions on the upper wing were reputed to be liable to collapse if the aircraft was dived too sharply.