O/400

The Standard O/400 was a two‑seat, single‑engine biplane developed by the Standard Aircraft Corporation in the United States during World War I. First flown in early 1917, the O/400 evolved from the earlier Sloane 75 and Model D series, incorporating a more powerful 400 hp (298 kW) Hall‑Scott A-5 engine that gave the type its designation. Its wooden frame, fabric covering, and equal‑span wings were typical of the era, while the staggered wing arrangement and generous wing area provided excellent lift and stability at low altitude. The aircraft could reach a top speed of about 115 mph (185 km/h) and carried a modest bomb load of up to 200 lb, making it valuable for reconnaissance, artillery spotting, and light bombing missions on the Western Front. Over 2,500 O/400s were built, many of them supplied to Allied air services, and the type became one of the most widely used American combat aircraft of the war. Its straightforward construction and reliable performance helped standardize mass‑production techniques that influenced post‑war civilian trainers, cementing the O/400’s lasting impact on early aviation development. Several surviving examples are displayed in museums across the United States, where they continue to illustrate the transition from wartime innovation to peacetime aviation training.

Standard Aircraft Corporation

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Design & Classification