B-3

The Keystone B‑3 was a United States Army Air Corps biplane bomber produced by the Keystone Aircraft Corporation in the early 1920s. Developed from the earlier LB‑5 and LB‑6 models, the B‑3 first flew in 1921 and entered service in 1922 as the third production variant of Keystone’s line of “pursuit‑type” bombers. Powered by a single 420 hp Liberty L‑12 V‑12 engine, the aircraft featured a wooden frame covered with fabric, a two‑seat open cockpit, fixed tailskid landing gear, and equal‑span staggered wings equipped with ailerons on both upper and lower surfaces. Its bomb load consisted of up to 2,000 pounds of ordinance carried in external racks beneath the lower wings, while defensive armament comprised a forward‑firing .30‑caliber machine gun and a flexible gun positioned in the rear cockpit. Although modest by later standards, the B‑3’s straightforward construction and reliable performance made it a workhorse for bomber training, reconnaissance, and night‑flight experiments throughout the 1920s. The type helped illustrate the tactical potential of dedicated medium bombers and provided valuable data that guided the transition to all‑metal monoplanes such as the Martin B‑10, marking a pivotal step in the evolution of American military aviation.