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.

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-8AM 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.

Name

Dates

Replaced

Alongside

Replaced by

1st Bombardment

1938-42

B-10

 

B-17

2nd Antisubmarine

1942

 

B-17, B-34

B-24

2nd Bombardment

1940-41

-

-

B-26

2d search attack

1942-43

B-25

 

B-24

3rd Bombardment

1940-42

-

-

LB-30/ B-17/ B-24

3rd search attack

1942-43

-

-

B-24

4th anti-submarine

1941-43

-

-

B-24

4th Bombardment

1941

 

PT-17, LB-30

1941-42

4th Search Attack

1942-43

-

A-20, B-24, B-34, B-17

 

4th Tactical Recon

1943-45

Loads

Loads

Loads

5th Bombardment

1938-42

B-10

 

B-24

5th Liaison

1942-43

Loads

Loads

Loads

6th Antisubmarine

1941-43

-

B-25, A29, B-24

?B-24

6th Bombardment

1940-41

YB-17

B-17

B-17

6th Fighter

1942

Many

Many

Many

7th Bombardment

1941

 

PT-17, LB-30

B-17

8th Bombardment

1939-40

A-17

Many

Many

9th Bombardment

1937-1940

B-10

B-17 overlap

B-17

10th Bombardment

1940-43

B-17, A-17

 

B-25

11th Bombardment

1937-40

B-10

B-17 overlap

B-17

12th Bombardment

1940-44

-

B-25 late

-

13th Bombardment

1939-41

A-17

B-12, A-20

B-25

14th Bombardment

1940-41

Many

-

B-17

18th Bombardment

1941

-

PT-17, LB-30

B-17

19th Bombardment

1940-41

-

-

B-26

20th Bombardment

c.1936-42

Many

Many

Many

21st Bombardment

1941

-

YB-17

A-29

21st Troop Carrier

1942

Many

Many

Many

22nd Antisubmarine
46th Bombardment when formed

1941-42

-

-

A-29

22nd Bombardment

1939-40

-

A-17

B-17

22nd Troop Carrier

1942

-

Many

Many

23rd Antisub
formed as 76th Bombardment

1941

-

-

B-26

24th Bombardment

1940-42

-

Many

-

25th Bombardment

1938-42

Many

Many

Many

26th Bombardment

1940-42

A-12

B-17 overlap

B-17

27th Bombardment

1941

-

-

A-29

28th Bombardment

1941

B-10

-

B-17

29th Bombardment

1941-42

-

-

A-17

30th Bombardment

c.1940?

B-10

 

B-17

31st Bombardment

1937-42

Varied

-

B-17

32nd Bombardment

c.1940?

B-10

-

B-17

33rd Bombardment

1940-41

-

-

B-26

34th Bombardment

1939-40

Varied

-

B-23

35th Bombardment

1941-43

-

-

B-25

36th Bombardment

1940-42

-

-

B-17

37th Bombardment

1940-41

A-17

 

B-25

38th Bombardment

1941-42

YB-17

-

Many

1st Observation
later 41st Photographic Reconnaissance

1942-44

Varied

Varied

Varied

42nd Bombardment

1940-41

Varied

-

B-17

43rd Bombardment

1940-41

-

B-17

B-17

86th Recon (later 43rd)

1942-42

Varied

Varied

Varied

44th Bombardment

1941-42

-

-

B-17

45th Bombardment

1941-42

-

-

LB-30

47th Bombardment

1941

 

PT-17

A-20

48th Bombardment

1941-42

 

A-29

B-25

49th Bombardment

c.1940?

 

Varied

B-17

54th Bombardment

1940

B-4

-

B-23

59th Bombardment

1943-44

A-20

B-25

-

63rd Bombardment

1941-42

 

B-17, B-25, LB-30

 

64th Bombardment

1941-42

-

-

B-17

66th Bombardment

1941-42

-

-

B-24

69th Bombardment

1941

-

-

B-26

71st Bombardment

1941

-

-

B-26

72nd Bombardment

1939-42

B-12

B-17

B-17

73rd Bombardment

1939-42

A-17

 

B-26

74th Bombardment

1939-42

Varied

-

B-17

75th Bombardment

1941-42

-

-

A-29, B-26

77th Bombardment

1941, 1942-43

-

B-26

B-25

81st Bombardment

1941-42

-

-

B-25

82nd Bombardment

1941-42

-

PT-17

B-25

83rd Bombardment

1941-42

-

B-23

B-25

84th Bombardment

1941-42

-

-

A-20

85th Bombardment

1941-42

-

A-20

A-20

86th Bombardment

1941-42

-

-

A-20

89th Bombardment

1941

-

A-18

A-20

90th Bombardment

1939-41

A-17

-

A-20

93rd Bombardment

c.1939

 

-

B-17

95th Bombardment

1939-40

A-17

-

B-23

96th Bombardment

c.1936

B-6 plus others

Varied

B-17

98th Bombardment

1942

-

-

B-17

99th Bombardment

1938-42

B-10

-

B-25, B-26, B-17

39th Recon (becomes 101st Bombardment Photographic

1943-44

Many

Many

Many

108th Reconnaissance

1943

Many

Many

Many

121st Liaison

1941-42

Many

Many

Many

313rd Bombardment

1942

 

A-20, B-25

B-26

348th Fighter

c.1943-44

Many

Many

Many

373rd Bombardment

1942

-

-

B-24

374th Bombardment

1942

-

-

B-24

375th Bombardment

1942

-

-

B-24

390th Bombardment

1942

-

A-29

B-26

392nd Bombardment

1941

-

B-17

LB-30, B-24

394th Bombardment

1938-41

B-12, P-12

-

B-17

395th Bombardment

1941-43

-

Loads

B-17, B-29

396th Bombardment

1941-42

-

LB-30, A-29

B-25

397th Bombardment

1938-42

B-10

-

B-17

403rd Bombardment

1941

-

B-17, A-29

B-17, B-24

405th Bombardment

1941

-

PT-13

B-26

406th Bombardment

1941-43

=

B-26, A-20

B-24, B-25

408th Bombardment

1937-41

B-10

Varied

B-25, B-26

411th Bombardment

1937-41

B-10, OA-4, OA-5

Varied

B-17, A-29

417th Bombardment

1939-44

-

B-25 1943-44

 

427th Bombardment

c.1936-41

P-26

Many

B-17

429th Bombardment

1940-42

Many

Many

B-17

430th Bombardment

1938-42

B-10 plus many

 

B-17, B-24, B-25, B-26

431st Bombardment

1938-41

B-12

-

B-17

432nd Bombardment

1940

-

-

B-23

434th Bombardment

1941-42

-

B-23

B-25

436th Bombardment

1937-40

Varied

-

B-24

88th Bombardment (later 495th Fighter)

1941

-

-

A-20

16th Bombardment (Light) late 522nd Fighter

1940-41

-

A-16

A-20, A-24

17th Bombardment (Light) later 523rd Fighter

1940-41

-

-

A-24, A-20

91st Bombardment (light) late 524th Fighter

1941

-

-

A-24

58th Bombardment (light) later 531st Fighter

19410-42

-

-

A-20

39th Bombardment (Medium) later 819th Bombardment

1941-42

-

B-25

A-20

41st later 827th Bombardment

1941

-

-

B-25

80th later 835th Bombardment

1942-43

A-20, DB-7

-

B-25

79th later 839th Bombardment

1941-42

-

Varied

Varied

78th late 851st

1942-43

-

A-20, DB-7

B-24

522nd later 855th

1942-43

-

B-26

B-24

517th later 859th

1943

L-49, O-46, O-47

 

B-25, B-24

92nd later 867th Bombardment

1941

-

Varied

Varied

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

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How to cite this article: Rickard, J (7 September 2015), Douglas B-18 Bolo , http://www.historyofwar.org/articles/weapons_douglas_B-18_bolo.html

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