B-18 Bolo

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Image:Douglas B-18 Castle.jpg The Douglas B-18 Bolo was a United States Army Air Corps and Royal Canadian Air Force bomber of the late 1930s and early 1940s based on the Douglas DC-2.

1 History
2 Surviving aircraft
3 Variants and Design Stages
4 Operators
5 Specifications (B-18A)
6 Reference
7 External links
8 Related content

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History

In 1934, the United States Army Air Corps put out a request for a bomber with double the bomb load and range of the Martin B-10, which was just entering service as the Army's standard bomber. In the evaluation at Wright Field the following year, Douglas showed its DB-1. It competed with the Boeing Model 299 (later the B-17 Flying Fortress) and Martin Model 146. While the Boeing design was clearly superior, the crash of the B-17 prototype (caused by taking off with the controls locked) removed it from consideration. During the depths of the Great Depression, the lower price of the DB-1 ($58,500 vs. $99,620 for the Model 299) also counted in its favor. The Douglas design was ordered into immediate production in January 1936 as the B-18.

Image:Douglas B-18A AF.jpg The DB-1 design was essentially the same as the DC-2, with several modifications. The wingspan was 4.5 ft (1.4 m) greater. The fuselage was deeper, to better accommodate bombs and the six-member crew; the wings were fixed in the middle of the cross-section rather than to the bottom, but this was due to the deeper fuselage. Added armament included nose, dorsal, and ventral gun turrets. The bomber used two Wright R-1820-45 ‘Cyclone 9’s, of 930 hp (694 kW) each.

The initial contract called for 133 B-18s (including DB-1), using Wright radials. The last B-18 of the run, designated DB-2 by the company, had a power-operated nose turret. This design did not become standard. Additional contracts in 1937 (177 aircraft) and 1938 (40 aircraft) were for the B-18A, which had the bombardier’s position further forward over the nose-gunner's station. The B-18A also used more powerful Wright R-1820-53 engines of 1,000 hp (746 kW).

By 1940, most Army bomber squadrons were equipped with B-18s or B-18As. Many of those in the 5th Bomb Group and 11th Bomb Group in Hawaii were destroyed in the attack on Pearl Harbor.

Image:Douglas B-18B Pima.jpg B-17s supplanted B-18s in first-line service in 1942. Following this, 122 B-18As were modified for anti-submarine warfare. The bombardier was replaced by a search radar with a large radome. Magnetic anomaly detection (MAD) equipment was sometimes housed in a tail boom. These aircraft, designated B-18B, were used in the Caribbean on anti-submarine patrol. Two aircraft were transferred to Força Aérea Brasileira in 1942. The Royal Canadian Air Force acquired 20 B-18As (designated the Douglas Digby Mark I), and used them for patrols also. Bolos and Digbys sank four submarines during the course of the war.

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Surviving aircraft

Only five B-18s still exist, preserved in museums in the United States:

B-18 s/n 37-0029, at Castle Air Museum, Atwater, California.
B-18A s/n 37-469, at National Museum of the United States Air Force, Wright-Patterson AFB, Ohio.
B-18A s/n 39-25, at Wings Over the Rockies Air and Space Museum, Denver, Colorado.
B-18B s/n 37-505, at McChord Air Museum, McChord AFB, Washington.
B-18B s/n 38-593, at Pima Air & Space Museum Tucson, Arizona.

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Variants and Design Stages

DB-1—Prototype; first of B-18 production run. (×1)
B-18—Initial production version. (×131, or 133)
- B-18M—Bomb gear removed from B-18 to serve as trainer.
DB-2—Powered nose turret prototype; last of B-18 production run. (×1)
B-18A—B-18 with more powerful Wright R-1820-53 engines, bombardier’s station moved. (×217)
- B-18AM—Bomb gear removed from B-18A to serve as trainer.
B-18B—Antisubmarine conversion. (×122)
B-18C—Antisubmarine conversion. (×2)
XB-22—Improvement on B-18 using Wright R-2600-3 radial engines (1,600 hp, 1194 kW); never built, largely due to better light bombers such as the B-23 Dragon.
C-58—Transport conversion.
Digby Mark I—Royal Canadian Air Force modification of B-18A.