Douglas production line at the Santa Monica Airport
The Douglas DB-7/A-20 attack bomber was a twin-engined, mid-wing monoplane equipped with tricycle landing gear and powered by either Pratt & Whitney Twin Wasp or Wright Cyclone engines of various sub-types. It featured two three-bladed Hamilton Standard propellers and could accommodate a crew of two to four, depending on the model. Douglas manufactured the aircraft at its El Segundo, Long Beach, and Santa Monica facilities between mid-1939 and late 1944, with additional production at Boeing in Seattle during 1941 and 1942. In total, 7,478 units were produced.
The empty weight of the aircraft increased from about 11,700 lb (5,300 kg) in the DB-7 model to nearly 17,000 lb (7,700 kg) in the A-20G model, with the absolute maximum overload gross weight rising from just over 15,000 lb (6,800 kg) to nearly 27,000 lb (12,240 kg).
The aircraft was primarily constructed from aluminum alloy. In the early 1930s, German engineers developed the first heat-treatable aluminum alloy with about 4 percent copper, using it in dirigible frame construction. This alloy became widely known as ‘dural,’ ‘duraluminium,’ or ‘dural aluminum.’ Later, the American company Alcoa introduced the ‘alclad’ process, producing aluminum alloy sheets with a layer of high-purity aluminum, typically 5.5 percent thick on each side, to prevent corrosion. This process became standard in American aircraft production. The A-20 used 24S alclad alloy (now known as 2024), which consisted of 4-5 percent copper, 1.5 percent magnesium, 0.6 percent manganese, and the remainder aluminum.