Boulton & Paul Bolton The Boulton & Paul P . 15 Bolton was a one - off experimental twin - engined reconnaissance biplane ordered by the Air Ministry to sustain Boulton & Paul ' s development of steel framed aircraft early in the 1920s . It was the RAF ' s first metal - framed aircraft . Design and development . Just after the end of the World War I the Air Ministry were keen to explore the use of all - steel airframes , partly because during the war spruce stocks had been seriously reduced . They were aware of Boulton & Paul ' s all - steel - framed , though probably unflown P . 10 and the claims of the company designer , John North that such aircraft could be 10 % lighter than their wooden framed equivalents . They therefore issued specification 4 / 20 for a steel framed version of the Boulton Paul Bourges twin - engined reconnaissance bomber and ordered one prototype , so that Boulton & Paul could continue to develop such structures . The P . 15 Bolton was the result . Despite its later type number , the Bolton was ordered and flew before the more unusual but equally steel framed P . 12 Bodmin . Thus the sole Bolton , serial " J6584 " was the first metal framed aircraft developed for the Royal Air Force . In general terms the Bolton was similar to the Bourges , though larger all round ; both were twin - engined , three bay biplanes with equal span , constant chord wings with no sweep or stagger . Both carried ailerons on upper and lower wings , though the wingtips of the Bolton were cut off square in the later Boulton & Paul fashion and lacked the protruding balances of the earlier machine . The interplane struts were quite wide chord , their twin triangular members covered in fabric . There were supporting sloping struts from the midpoints of the wing midsection to the upper fuselage longerons . The two 450 hp ( 336 kW ) Napier Lion engines were mounted just inboard of the inner interplane struts , not directly onto the lower wing but rather on ( for the top part of the engine was uncovered for air cooling ) a little nacelle which had at the front and below the propeller boss , a small radiator . Four - bladed propellers were fitted . The Bolton ' s fuselage was square sided except behind the wings where an extra central member made the upper section triangular . This was done to enhance the downward field of fire from the dorsal position . The pilot ' s cockpit was forward of the wings and in the nose there was another gunner ' s position . This crew member doubled as bomb - aimer from a windowed position slightly further forward in the lower fuselage , in a nose that looked much like that of the Bodmin . The tailplane was mounted at the top of the fuselage , with a fin and rudder that projected below the fuselage , protected by a tailskid . The rudder had a large horn balance that overhung the fin and its unusual forward extension that acted as a trimming surface . The single axle undercarriage was of much narrower track than that of the Bourges , mounted just inboard of the engines on pneumatically sprung and damped legs in the manner of the Bodmin . A pair of members converged from the legs to a single forward wheel , there to prevent nose - overs . The Bolton first flew , piloted by Frank Courtney in September 1922 . Its career and performance remain largely hidden by official secrecy , though an estimated maximum speed of 130 mph ( 209 km / h ) at 10 , 000 ft ( 3 , 048 m ) did emerge . In a review of British aircraft in May 1924 , some 20 months after the first flight , its name is listed in the index but without a page number . In contrast , the " Postal " Bodmin , though only just flown gets a paragraph . Nonetheless , Boulton & Paul ' s growing expertise in metal - framed twin - engined aircraft was rewarded by orders for seven Bugles and led to the Sidestrands and Overstrands that achieved squadron service , albeit in small numbers .