During the late 1930s and early 1940s, the Douglas B-18 Bolo served with both the United States Army Air Corps and the Royal Canadian Air Force (referred to as the Digby).
The Bolo was developed by the Douglas Aircraft Company, based on their DC-2 model, and was designed to replace the Martin B-10 bomber.
However, when compared to 1940 standards, the B-18 was considered slow, had an inadequate defense system, and could only carry a small bomb load.
Despite these limitations, a B-18 successfully sank a German U-boat, U-654, in the Caribbean on August 22, 1942, becoming one of the first USAAF aircraft to do so.
By 1942, the remaining B-18s were primarily used for antisubmarine, training, and transport purposes.
In 1934, the United States Army Air Corps requested a twin-engine heavy bomber with double the bomb load and range of the Martin B-10.
During the evaluation process at Wright Field the following year, Douglas offered its DB-1, which was competing against the Boeing Model 299 (later developed into the Boeing B-17 Flying Fortress) and Martin 146.
Despite being favoured, the Boeing Model 299 was eliminated from consideration due to its four engines, and the prototype’s crash (caused by taking off with the controls still locked) put its purchase on hold.
The Martin 146 was also not seriously considered as it was only a minor improvement on the B-10.
The DB-1 was ultimately chosen due to its lower cost of $58,500 compared to the Model 299’s $99,620 and was ordered into production in January 1936 as the B-18.
The DB-1 design was modified from the DC-2, with the wingspan being increased by 4.5 feet (1.4 meters), the fuselage becoming narrower and deeper, and the wings being moved to a mid-wing position to allow for an enclosed bomb bay.
Additional armament included manually operated nose, dorsal, and ventral gun turrets.
Although Preston Tucker’s firm received a contract to supply Tucker with remote-controlled gun turrets, they were unsuccessful and never used in service. Variants DB-1 Manufacturer’s designation for prototype, first of B-18 production run, 1 built. B-18 Initial production version, 131 or 133 built. B-18M Trainer B-18 with bomb gear removed. DB-2 Manufacturer’s designation for a prototype with powered nose turret; last of B-18 production run, 1 built. B-18A B-18 with more powerful Wright R-1820-53 engines and relocated bombardier’s station, 217 built. The manufacturer’s designation was DB-4. B-18AM Trainer B-18A with bomb gear removed. B-18B in flight, showing Magnetic Anomaly Detector in the tail and radar in the nose. B-18B Antisubmarine conversion, 122 converted by adding a radar and magnetic anomaly detector. B-18C Antisubmarine conversion, 2 converted. Fixed forward-firing .50 in (12.700 mm) machine gun,
Starboard side of the fuselage near lower nose glazing. XB-22 Improved B-18 with 1,600 hp (1,200 kW) Wright R-2600-3 radial engines. Not built, due to better designs being available. C-58 Transport conversion. Digby Mark I Royal Canadian Air Force modification of B-18A. Named as the RAF Digby. Specifications Crew Six Length 57 ft 10 in (17.63 m) Wingspan 89 ft 6 in (27.28 m) Height 15 ft 2 in (4.62 m) Wing area 959 sq ft (89.1 m2) Airfoil Root NACA 2215 Tip NACA 2209 Empty weight 16,320 lb (7,403 kg) Gross weight 24,000 lb (10,886 kg) Max take-off weight 27,673 lb (12,552 kg) Powerplant 2 × Wright R-1820-53 Cyclone 9-cylinder air-cooled radial piston engines, 1,000 hp (750 kW) each Propellers 3-bladed fully-feathering Hamilton Standard Hydromatic propellers Performance Maximum speed 216 mph (348 km/h, 188 kn) at 10,000 ft (3,000 m) Cruise speed 167 mph (269 km/h, 145 kn) Range 900 mi (1,400 km, 780 nmi) Ferry range 2,100 mi (3,400 km, 1,800 nmi) Service ceiling 23,900 ft (7,300 m) Time to altitude 10,000 ft (3,000 m) in 9 minutes 54 seconds Wing loading 25 lb/sq ft (120 kg/m2) Power/mass 0.0833 hp/lb (0.1369 kW/kg) Armament Guns 3 × 0.30 in (7.62 mm) machine guns Bombs 2,000 lb (910 kg) normal; 4,400 lb (2,000 kg) maximum Avionics B-18B (only) SCR-517-T-4 ASV radar Mark IV Magnetic anomaly detector (MAD).
Sources Douglas B-1 Bolo, The Ultimate Look: From Drawing Board to V-boat Hunter-William Wolf, McDonnell Douglas aircraft since 1920: Volume I-René J Francillon, San Diego Air and Space Museum Archive, The National Museum of the U.S. Air Force.