Why did Bristol build the M.R.1 in metal?

Bristol's first sketches for metal aircraft dated back to 1914, but official interest did not appear until the rise in aircraft production during the First World War began to put pressure on the supply of high-quality timber. Even in the early days of powered flight, some manufacturers were starting to consider using metal in airframes to replace wood. Metal structures, even metal frames covered with fabric, offered greater strength for handling and transport, as well as better resistance to tropical climates. In 1916, Bristol's designer Frank Barnwell presented the design for a two-seat metal reconnaissance aircraft, the M.R.1 — for Metal Reconnaissance — and secured a contract for two evaluation aircraft.

Barnwell borrowed from naval experience and used duralumin sheet, varnished to prevent corrosion, from which he built the fuselage in four sections. The construction used a double skin: a smooth outer covering riveted over an inner skin corrugated lengthwise.

The aluminium spars proved difficult to make sufficiently rigid, and Bristol subcontracted their manufacture to The Steel Wing Company, in Gloucester, which had built experimental steel wings for other aircraft. With the first M.R.1's fuselage finished before the wings, Bristol decided to fit a conventional set of wooden wings, with ailerons only on the upper planes, for the flight trials in mid-1917; they performed well and the aircraft was delivered to the Air Board in October 1917. The second M.R.1 did not fly until late 1918, when the metal wings were finally ready.