Douglas B-18 Bolo
Douglas developed the B-18 to replace the Martin B-10 as the U.S. Army Air Corps' standard bomber. Based on the Douglas DC-2 commercial transport, the prototype B-18 competed with the Martin 146 (an improved B-10) and the four-engine Boeing 299, forerunner of the B-17 Flying Fortress, at the Air Corps bombing trials at Wright Field in 1935. Although many Air Corps officers judged the Boeing design superior, the Army General Staff preferred the less costly Bolo (along with 13 operational test YB-17s).
The B-18 was developed from the successful DC-2 commercial airliner. In 1935 a design competition and "fly-off" was held to select a replacement for the Martin B-10/12 then in service with the USAAC. Competitors were the Douglas DB-1, Martin 146 (an improvement of the B-10 design) and Boeing Model 299. The Douglas design was selected, designated B-18 and contracts awarded for 82. The order was increased to 132 by June of 1936.
The second version, designated B-18A, appeared in 1937 with a revised nose with extensive glazing in which the bomb-aimer/navigator sat above and ahead of the nose gun, which was housed in a ball-type turret. 255 of this version were ordered. Only 217 were delivered as B-18As; the final 38 were delivered as B-23s, an almost total redesign.
Though equipped with inadequate defensive armament and underpowered, the Bolo remained the Air Corps' primary bomber into 1941. Thirty-three B-18s were based in Hawaii with the 5th Bombardment Group and 11th Bombardment Group. In the Philippines, twelve were assigned to the 28th Bombardment Squadron. Additional B-18s were based in Panama and the Caribbean and at three bases in the U.S.
The Japanese destroyed some B-18s during the surprise attacks on December 7, 1941 on Oahu and in the Philippines. The few remaining played no significant role in later operations. By early 1942, improved bombers like the B-17 replaced the Bolo as first-line bombardment aircraft. But, many B-18s were then used as transports, or modified as B-18Bs for anti-submarine duty.
Douglas built 133 B-18s were built and 217 B-18A .