The Douglas B-18 Bolo served with the Royal Canadian Air Force and the United States Army Air Corps (USAAC) in the late 1930s and early 1940s. The Douglas Aircraft Company-made Medium Bomber was developed based on the Douglas DC-2 and was built to replace the Martin B-10.
It was among the bombers used to sink a German U-boat, U-654 in the Caribbean in August 1942.
The Bolo was considered to be underpowered. Its bomb load was considered too small alongside its inadequate defensive armament.
The development of The Douglas B-18 Bolo started in 1934 when the USAAC requested for a medium bomber with twice the bomb load and range of the Martin B-10, which just entered the service as the Standard Bomber for the Army. This prompted actions from different designers and manufacturers, and the following year at Wright Field, Douglas showed its DB-1 design.
The lower price of the Douglas DB-1, in contrast to the competing Boeing Model 299 counted in its favor and thus, in January 1936, The Douglas design was ordered into immediate construction as the B-18.
The B-18 was based on the DC-2, although it had several modifications. Its wingspan was 4.5ft bigger. In order to contain bombs and the six-member crew, the fuselage was made deeper. Due to the deeper fuselage, the wings were attached in the middle of the cross-section instead of the deeper fuselage. The ventral gun turrets, nose, dorsal were also added to the armament.
It had a speed of 215 mph, cruising speed of 167 mph, and a range of 850 miles. It was propelled by 2 Wright R-1820-53 Radial Piston engines which dissipated 1,000 Horsepower each.
It’s armament comprised of a .30 caliber machine gun in the nose position, another .30 caliber machine gun in the central position, and another .30 caliber machine gun in the dorsal position. There were two .50 caliber heavy machine guns serving as anti submarine defense.
However, the deficiencies of the B-18 would be made evident during the Pacific war as most B-18s in the Philippines and Hawaii were destroyed by the Japanese. The surviving ones played no significant roles later on.
The B-18 was regarded as an obsolete commodity because of the technology and progression of the war itself. It was considered underpowered for the growing USAAC requirements. Its bomb load was surpassed by newer developments and these reduced its tactical usefulness in the short term.
Some of the Bolos after being modified with anti-submarine weaponry were used in the Caribbean on anti-submarine patrol.
The Bolos were still used within the United States to train bomber crews in large aircraft flight and level bombing while getting used to high altitude travel. Some B-18s were used as make-shift transports after being stripped of their warfighting capacities.
In all, the Douglas B-18 Bolo had a few well-known variants namely: DB-1 which was the prototype, DB-18 which became the first production version, B-18M which served as a trainer, DB-2 which was the last of the B-18 run, B-18A which was essentially a B-18 with more effective Wright R-1820-53 engines, B-18AM which became a trainer aircraft, B-18B and B-18C which were anti-submarine conversions, C-58 which was a transport conversion and Digby mark I which was the Royal Canadian Air Force modification of B-18A.
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