Douglas B-18A Bolo

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.

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, then 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. The Douglas design was ordered into immediate production in January 1936 as the B-18.

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.

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. The Royal Canadian Air Force acquired 20 B-18As (designated the Douglas Digby Mark I), and used them for patrols also.

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.

Specifications (B-18A)

General Characteristics

• Crew: 6
• Length: 57 ft 10 in (17.6 m)
• Wingspan: 89 ft 6 in (27.3 m)
• Height: 15 ft 2 in (4.6 m)
• Wing area: 959 ft² (89.1 m²)
• Empty: 16,321 lb (7,400 kg)
• Loaded: 22,123 lb (10,030 kg)
• Maximum takeoff: 27,500 lb (12,600 kg)
• Powerplant: 2× Wright R-1820-53, 1,000 hp (750 kW)

Performance

• Maximum speed: 215 mph (346 km/h)
• Combat Range: 1,150 miles (1,850 km)
• Ferry Range: 2,100 miles (3,400 km)
• Service ceiling: 23,900 ft (7,280 m)
• Rate of climb: 1,030 ft/min (310 m/min)
• Wing loading: 23.1 lb/ft² (113 kg/m²)
• Power/Mass: .090 hp/lb (.15 kW/kg)

Armament

• 3× .30-calibre machine guns
• 4,500 lb (2,200 kg) of bombs

References and External links

• USAF Museum description of B-18

Related Content

Related development: Douglas DC-2

Designation sequence: XB-15 - XB-16 - B-17 - B-18 - XB-19 - Y1B-20 - XB-21 - XB-22 - B-23 - B-24 - B-25

Related Lists List of military aircraft of the United States - List of bomber aircraft