Douglas DB-1 / B-18 Bolo / DB-2 / Digby Mk I / C-58
With a 1934 US Army Air Corps requirement for a bomber with greater capability than their Martin B-10, Douglas drew on engineering experience of the DC-2 commercial transport.
Private-venture prototypes to meet the US Army's requirements were evaluated at Wright Field, Ohio, in August 1935, these including the Boeing Model 299, Douglas DB-1 and Martin 146. The first was built as the B-17 Flying Fortress, the last was produced as an export variant of the Martin B-10/B-12 series, and the Douglas DB-1 (Douglas Bomber 1) was ordered in January 1936 into immediate production under the designation B-18.
Derived from the commercial DC-2, the DB-1 prototype retained a basically similar wing, tail unit and powerplant. There were two differences in the wing: while retaining the same basic planform as the DC-2, the DB-1 had a 1.37m increase in span and was mounted in a mid-wing instead of low-wing position on an entirely new fuselage. The fuselage was deeper than that of the commercial transport to provide adequate accommodation for a crew of six, and to include nose and dorsal turrets, a bomb-aimer's position, and an internal bomb bay. There was a third gunner's position, with a ventral gun discharging via a tunnel in the underfuselage structure. Power was from two 694kW Wright R-1820-45 Cyclone 9 engines.
133 B-18s were covered by the first contract, including the single DB-1 which had served as a prototype. Production aircraft, which had the type name Bold, had equipment changes producing an increase in the normal loaded weight, and more-powerful Wright R-1820-45 radials. The last B-18 to come off the production line differed by having a power-operated nose turret, and carried the company identification DB-2, but this feature did not become standard on subsequent production aircraft.
A second contract covered 217 B-18A aircraft, placed in June 1937 (177) and mid-1938 (40). This version differed by having the bomb-aimer's position extended forward and over the nose-gunner's station, and the installation of more-powerful Wright R-1820-53 engines. Most of the USAAC's bomber squadrons were equipped with B-18s or B-18As in 1940, and the majority of the 33 B-18As which equipped the USAAC's 5th and 11th Bomb Groups, based on Hawaiian airfields, were destroyed when the Japanese launched their attack on Pearl Harbor.
When in 1942 B-18s were replaced in first-line service by B-17s, 122 B-18As were equipped with search radar and magnetic anomaly detection (MAD) equipment for deployment in the Caribbean on anti-submarine patrols under the designation B-18B. The Royal Canadian Air Force also acquired 20 B-18As which, under the designation Digby Mk I, were employed on maritime patrol. The designation B-18C applied to two other aircraft reconfigured for ASW patrol. Another two aircraft were converted for use in a transport role under the designation C-58, but many others were used similarly without conversion or redesignation.
Engines: 2 x Wright R-1820-53 Cyclone 9, 746kW / 986 hp
Max take-off weight: 12552 kg / 27673 lb
Empty weight: 7403 kg / 16321 lb
Wingspan: 27.28 m / 89 ft 6 in
Length: 17.63 m / 57 ft 10 in
Height: 4.62 m / 15 ft 2 in
Wing area: 89.65 sq.m / 964.98 sq ft
Wing loading: 28.70 lb/sq.ft / 140.0 kg/sq.m
Max. speed: 187 kts / 346 km/h / 215 mph
Cruise speed: 145 kts / 269 km/h / 167 mph
Service ceiling: 7285 m / 23900 ft
Range: 1043 nm / 1937 km / 1204 miles
Armament: 3 x 7.62mm (0.30in) machine-guns, 2948kg of bombs