Douglas B-18 Bolo

The Douglas B-18 Bolo was a bomber based on the DC-2 airliner and played an important part in the expansion of the USAAC, despite being obsolete by the time the United States entered the Second World War.

In May 1934 the Army Air Corps issued a specification for a new bomber. The aircraft would have to be able to carry a payload of 2,000lb over a range of 1,020 miles and preferably 2,200 miles, with a top speed of at least 200mph and ideally above 250mph. Douglas, Martin and Boeing all produced aircraft to this specification.

Douglas B-18A in Flight

The Douglas design was partly based on the successful DC-2 airline, using the wings from that aircraft and an enlarged version of the tail. It had a new deeper fuselage with room for an internal bomb bay in the centre section. The prototype has a short flat nose, with the bombardier in a small space at the base and a gun position at the top. The aircraft had a crew of three - two pilots, bombardier/ navigator and three gunners. It was armed with three manually operated 0.30in machine guns, one in the nose, one in a dorsal position and one fired through a ventral hatch.

The prototype was powered by two 850hp Wright R-1820-G5 engines. It made its maiden flight in April 1935 and was delivered to the Army at Wright Field in August 1935. The army then tested it against the Martin 146 (an improved version of the Martin B-10) and the Boeing 299 (the prototype for the B-17 Flying Fortress). The Boeing design was the best of the three, with longer range, a bigger payload and more guns, but it was almost nearly twice as expensive. The Douglas design only just met the basic requirements, with a top speed of 220mph (against a target of 200mph) and a range of 1,030 miles (only ten miles over the target). Although the Air Corps's technical staff wanted the Boeing design, the General Staff preferred numbers, and in January 1936 an order was placed for 133 Douglas B-18s. The Boeing project was kept alive with an order for thirteen YB-17s.

The B-18 began to enter service in 1937, with early aircraft going to the 7th Bombardment Group in California, the 5th Bombardment Group on Oahu, the 38th Reconnaissance Squadron in California, the 18th Reconnaissance Squadron at Mitchel Field and the 21st Reconnaissance Squadron in Virginia. As the Air Force expanded during 1940 many of the new bombardment groups were equipped with the B-18 before converting to more modern types, in particular the B-17 Flying Fortress and B-24 Liberator.

The B-18 had a very brief combat career. In December 1941 there were 33 at Hickham Field on Hawaii and 12 at Clark Field in the Philippines. Most of these aircraft were destroyed during the initial Japanese attack, and the remaining aircraft in the Philippines had little impact on the course of the fighting.

During 1942 the B-18 had a second lease of life as a anti-submarine patrol aircraft, before once again being replaced by the B-24 during 1943. Soon afterwards the Navy took over responsibility for anti-submarine air patrols.

The surviving B-18s spent the rest of the war operating with training units or as transport aircraft.

Variants

B-18

The B-18 was the first production version of the aircraft. The original order for 133 B-18s included 131 aircraft completed as B-18s (serials 36-262 to 32-343, 36-431 to 36-446 and 37-1 to 37-33. The remaining two aircraft were made up of the prototype DB-1, which was brought up to B-18 standard and delivered as 37-51 on 28 February 1937, five days after the first of the production aircraft, and aircraft 37-34, which was completed as the DB-2 but then converted back to DB-2 standard.

The B-18 was similar to the prototype, other than the use of 930hp Wright R-1820-45 engines with wider propeller blades and new cowlings.

DB-2

The DB-2 (serial no 37-35) was built under the first contract. It had a new nose with a power operated turret and glazed bomb aimer's position below. The new nose wasn't a great success and the DB-2 was given a standard B-18 nose and delivered to the Air Corps.

B-18A

The B-18A saw the introduction of a new 'shark's nose', with the gun position and bomb aimer's positions swapped over. The bomb aimer now got a glazed position that was positioned at the top of the nose, while the gunner had a ball turret that was mounted below and behind the bomb aimer. The gunner thus had a good view down and forward, but a limited view upwards. The B-18A also got the 1,000hp Wright R-1820-53 engine, with fully feathering propellers. The first B-18A made its maiden flight on 15 April 1938.

A total of 217 B-18As were ordered in three batches (although all under one contract, AC9977). The first batch, of 177 aircraft (37-458 to 37-634) was ordered in June 1937. The second and third batches, with 40 aircraft between them (38-585 to 38-609 and 39-12 to 39-26) were ordered in 1938, using money from FY1939 and FY1939). Another 38 had originally been ordered as 39-27 to 39-64, but these aircraft were produced as the B-23 Dragon.

B-18M and B-18AM

In 1940 twenty-two B-18s and seventeen B-18As had some of their bomb shackles removed so they could carry larger bombers, and were redesignated as the B-18M and B-18AM respectively.

B-18B

The B-18B was the designation given to 122 B-18As that were converted into anti-submarine aircraft in 1942, after the US entry into the war left US coastal shipping very exposed to U-boat attack.

The main change was to replace the bomb aimers glazed now with a SCR-517-T-4 ASV radar set covered by a plastic radome. Some aircraft also got a Mk IV Magnetic Anomaly Detection kit located in a tail extension. The B-18B normally carried depth charges, but some were tested with gear that launched bombs backwards from under the wings. 

B-22

The B-22 was the designation given to a version of the B-18 that would have been powered by the 1,600hp Wright R-2600-3 engine

C-58

Two B-18As were converted into unarmed cargo aircraft and given the designation C-58.

Douglas Digby

The Douglas Digby was the name given to a number of B-18s that were ordered for the RCAF. In 1938 the RAF had rejected the B-18 as being underpowered, under-armed and over-priced, and had ordered the Lockheed Hudson instead. The RCAF took a more positive view of the B-18 and placed an order for twenty B-18s. These were delivered between 29 December 1939 and 22 May 1940 and were similar to the B-18A, but with British 0.303in machine guns.

B-18
Engine: Two Wright R-1820-45 Cyclones
Power: 930hp each
Crew: 6
Span: 89ft 6in
Length: 56ft 10in
Height: 15ft 2in
Empty weight: 15,750lb
Maximum take-off weight: 27,087lb
Max speed: 217mph
Cruising Speed: 167mph
Climb Rate: 1,355ft/ min
Service ceiling: 24,200ft
Endurance:
Range: 1,200 miles
Armament:  Three .30in machine gunes
Bomb load: 4,400lb max, 2,000lb normal

Help - F.A.Q. - Contact Us - Search - Recent - About Us -  Subscribe in a reader - Join our Google Group - Privacy