The Boulton & Paul P.37 Streamline was a design for a sesquiplane day bomber that was the first in a series of similar designs, none of which entered production.
The P.37 took advantage of a long series of wind tunnel experiments, Boulton & Paul having had a wind tunnel since the First World War. The P.37 was a sesquiplane, with a large upper wing and smaller lower wing. The upper wing had a span of 72ft and chord of 12ft, the lower wing had a smaller span and a chord of only 3ft. The small lower wing had a narrow chord and was attached to the fuselage. The larger upper wing was carried on a pylon that lifted it above the fuselage, in an attempt to reduce interference drag. The two Rolls-Royce F.XIS engines were carried on this upper wing. The upper wing was of equal chord, but it differed from the normal Boulton & Paul square tipped form - the outer front corners were still square, but the outer rear corners were curved.
The streamlined fuselage carried two crew sitting in tandem in front of the wing. The enclosed cockpit had a all-round vision canopy, although the view backwards would have been fairly poor.
The P.37's most unusual feature was its retractable skid undercarriage. This ran from just behind the nose to just in front of the centre of the fuselage, and was supported on three legs. Smaller outriggers were positioned below the lower wing. The surviving design plans don't say where the bombs would have been carried.
The same layout was used on a series of civil and military projects. The P.47 was a high speed mail carrier. The P.49 was a racing aircraft. The P.56 was a second mail carrier. Finally the P.63 was a high performance interceptor.