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Douglas B-18 Bolo

Medium Bomber Aircraft [ 1936 ]

The Douglas B-18 Bolo medium bomber made up a large part of the U.S. Army Air Force bomber squadrons in 1940.

Authored By: Staff Writer | Last Edited: 01/22/2017 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site.

In 1934, the American Douglas aircraft concern developed the DB-1 (also known as the "Douglas Bomber 1") to fulfill a United States Army Air Corps (USAAC) requirement for a long-range, medium-class bomber. The USAAC sought to replace its new fleet of gangly Martin B-10 bombers and utilize a newer platform with much improved capabilities. Douglas developed their DB-1 from their existing "DC-2" series commercial transport aircraft, a serviceable twin-engine development first flying in May of 1934 and seeing some total 200 aircraft produced. Retaining the former's wings (though lengthened somewhat), the DB-1 made use of a deeper fuselage for an internal bomb bay and applicable defensive weaponry was added. As such, the DB-1 was based highly on the experiences and technology of the DC-2 form, essentially becoming a "militarized" version of the transport. The prototype DB-1 was completed in 1935 and entered into a USAAC-sponsored competition that included the twin-engined Martin "Model 146" as well as the Boeing "Model 299". First flight for the Douglas prototype was recorded in April of 1935.

The Long Range Medium Bomber Competition

Up to this point, Martin earned the American military contract with the sale of its original B-10 (introduced in November of 1934) and the type served as the standard bomber for the USAAC. However, the USAAC was already looking for its replacement, resulting in Martin's submission into the competition of its enlarged B-10 version - the "Model 146". Boeing developed and submitted its "Model 299", an expensive and large four-engine platform that seemingly fit well into USAAC requirements for a new long-range bomber (itself eventually becoming the famous B-17 "Flying Fortress").

In the evaluations held at Wright Field during 1935, the three aircraft were reviewed by the USAAC. Representatives were noticeably high on the Boeing Model 299 thought the single prototype was lost in an accident eventually blamed on pilot error. The crash, therefore, disqualified the Model 299 from the competition altogether, leaving the Douglas B-18 as something of the frontrunner (little was mentioned of the Martin design). Additionally, the Boeing Model 299 proved a cost-prohibitive machine to the still budget-conscious USAAC (the Great Depression still had its hold on world economies during this time) and this furthered the DB-1 endeavor for a single example of the Douglas design cost nearly half of what it would take to procure a Boeing Model 299. The Douglas DB-1 design was therefore formally inducted into USAAC service as the B-18 "Bolo" to which 99 initial B-18 models were contracted. Interestingly - and despite the loss of the Boeing Model 299 in the competition - the USAAC also contracted for 13 YB-17 evaluation aircraft for additional study. Of note for Douglas was that the B-18 became the firm's first medium bomber design in the firm's history (ironically its history now tied to Boeing today).

Production and Operational Use

In 1937, 35 additional B-18 Bolos were contracted, bringing the USAAC inventory up well over 100. All of these early forms were powered by the Wright R-1820 series radial piston engine. A single version fitting a power-operated nose turret emerged as the last B-18 in this production run and known by Douglas as the "DB-2". In the late 1930s, another contract numbering 217 B-18s was placed, these being the improved B-18A with its forwarded bombardier's position over the nose gunner and delivered during the span of 1937 into 1939. Some 350 to 370 production B-18s were eventually procured overall.

Despite their rather outclassed status at the opening of World War 2, B-18 bombers were still serviceable platforms utilized to train up-and-coming bomber crews in the nuisances of large aircraft flight and level bombing while acclimating to high altitude travel. The B-18 presence was found within the United States borders as well as through various overseas deployments. In addition to their use as conventional bombers and trainers, B-18s (stripped of their warfighting capacities) were used as make-shift transports. Some were modified further for use as anti-submarine warfare (ASW) platforms and actively deployed along American coasts and over Caribbean waters during maritime patrols. In fact, a B-18 was credited with the first sinking of a German U-boat submarine (this in Caribbean waters) on August 22nd, 1942 - the U-boat being identified as "U-654". Eventually B-18s were replaced in number by the superior large-capacity Consolidated B-24 Liberator and the (more famous) Boeing B-17 Flying Fortress - two aircraft of what would become the "heavy hitters" of the United States Army Air Corps over both Europe and the Pacific.


In all, the B-18 existed in a few well-known variants. The single prototype was the aforementioned "DB-1" before becoming the 130 initial "B-18" production forms. With its bombing facilities removed, the "B-18M" served as a crew trainer. Douglas then developed the "DB-2" prototype with a powered nose turret to which a single example was completed. The "B-18A" was the next major production version with some 217 were built with the more powerful Wright R-1820-53 series radial piston engines. The bombardier's position was also revised for improved visibility, now moved out over the nose gunner's position. The "B-18AM" emerged from this production form as a crew trainer. The "B-18B" was the dedicated anti-submarine warfare platform and 122 were converted from existing airframes. Only two of the similar "B-18C" submarine-hunters were made, these having 2 x 0.50 caliber heavy machine guns added as forward-firing installations along the right fuselage side for strafing. A prototype B-18 was developed under the designation of "XB-22" and fitted with Wright R-2600-3 series radial piston engines of 1,600 horsepower each but this design never entered serial production. The USAAC transport version of the B-18 was known as the "C-58". The "Digby I" was the Canadian designation for its small supply of B-18s.©MilitaryFactory.com
The End of the Road

Ultimately, the cause of technology and progression of the war itself inevitably made the B-18 an obsolete commodity. She proved underpowered for the growing USAAC requirements and her inherent defensive machine gun network left much to be desired. Her bomb load was largely outclassed by newer developments elsewhere, shortening the tactical usefulness of the B-18 in the short term. Regardless, the B-18 served as the USAAC's standard medium bomber up until 1941 for she handled herself quite well, proving adept as absorbing damage while still being flyable (a common trait of nearly all World War 2-era bombers). During the early phases of World War 2, aircraft such as the B-18 proved vastly important across their defined roles for the building American war machine. B-18s were present (unfortunately as ground targets) during the Japanese surprise attack on Pearl Harbor on December 7th, 1941 which officially involved the United States in World War 2. Nearly all B-18s at Hickam Field in the US territory of Hawaii were lost in the attack.

By early 1942, with the US war machine now ramping up to feverish pitches, antiquated designs such as the B-18 gave way to more technologically superior and modern implements. Twenty B-18 Bolos served with Canadian air forces and were known under the RCAF designation of "Digby Mk I" while being formally classified as "reconnaissance bombers" in inventory. Brazil became the only other export operator of the B-18 (under the banner of the "1st Bomber Group") and maintained three examples actively until their retirement in post-war 1946. For the Americans, the B-18 served with no fewer than 22 bomber groups from Virginia to Hawaii as well as those units deployed in Panama, the Philippines, Puerto Rico and within South America.

B-18 Bolo Walk-Around

Externally, the Bolo managed a very distinctly stout appearance thanks to its oversized fuselage bay. The cockpit and bombardier positions were held at the extreme front of the fuselage, each area identified by its use of heavy framing but both offering strong views outside of the aircraft. Ordnance loads were held in the internal bomb bay making up the center of the fuselage. Wings were monoplane in design, rounded in typical 1930s fashion, and fitted as mid-mounts along the fuselage sides. Each wing was completed with an engine nacelle along their leading edges. The midway point of the fuselage also contained vision ports for the crew within and a dorsal and ventral machine gun or observation position. An access door was noted along the fuselage side aft of the main wing assemblies. The empennage was conventional in design with a single, rounded vertical tail fin and applicable rounded horizontal planes. The B-18 undercarriage was of the "tail dragger" sort, meaning it made use of two main landing gear legs and a small tail wheel. This, along with the deep fuselage, gave Bolos their rather noticeable "nose-up" appearance when at rest. Each main landing gear leg was finished with a large wheel and the legs recessed under each engine nacelle when the aircraft was in flight. The bomb bay doors were found along the aircraft's belly aft of the cockpit floor. Two-piece doors were used to keep ordnance in check as well as complete the aerodynamic form of the B-18. Each bomb bay door opened outboard of centerline as two-piece systems that folded over on one another. The Bolo was crewed by six personnel including two pilots, a dedicated bombardier and three machine gunners. Dimensionally, the aircraft exhibited a wingspan of 89 feet, 6 inches with a running length equal to 57 feet, 10 inches. She stood at 15 feet, 2 inches in profile. Overall weight was 27,000lbs when fully laden with an internal bomb load.

B-18 Cockpit

The cockpit of the B-18 consisted of two pilot seats in a side-by-side arrangement. The instrument panel dominated the forward view and contained nearly all of the available system gauges and switches. Each position held a conventional flight yoke wheel for control from either seat. Engine controls were clustered at a center console for equal reach from either position. Should the pilot become incapacitated during flight, the copilot could therefore resume control of the aircraft without having to shift out of position. Each position also held their own foot pedals. Vision out of the cockpit was relatively good aside from the heavy use of framing consistent with other aircraft of the time. The windowed panels allowed for clear vision ahead, above and to the sides of the aircraft. Both engine nacelles were clearly visible from the pilot's positions, allowing either personnel to respond to engine fires and the like.


The B-18 was defensed by 3 x 0.30 caliber machine guns. These lacked the general firepower inherent in the more potent 0.50 caliber Browning M2 heavy machine guns so prevalent in later US aircraft, ship and vehicles throughout the war. One machine gun was fitted in the nose with another in a dorsal position. The third was mounted to a ventral position. In addition to this defensive armament, the true "bread and butter" of any bomber was naturally its ability to carry bombs. The B-18 was listed to carry up to 2,000 to 4,500lbs of internal stores for such work - be they conventional drop bombs or naval depth charges as needed.


Power for the B-18 was supplied by a pair of Wright R-1820 series air-cooled radial piston engines supported within streamlined nacelles along the wings. Each engine was rated up to 1,000 horsepower of output depending on the powerplant model number (various R-1820s were used in B-18 production). This allowed for a maximum speed of 215 miles per hour (at approximately 15,000 feet) with a cruising speed of 167 miles per hour. Operational range was limited to 2,100 miles while the listed service ceiling maximized at 24,000 feet. The engines powered three-bladed metal propellers.

The B-18 Bolo Today

Today, only six examples of B-18s exist of the hundreds produced with five of these serving as static museum display pieces and one currently undergoing refurbishment. Appropriately, one of these can be found at the National Museum of the United States Air Force at Wright-Patterson Air Force Base in Dayton, Ohio - near the birthplace of the Bolo.©MilitaryFactory.com
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Douglas Aircraft Company - USA
Brazil; Canada; United States
Operators National flag of Brazil National flag of Canada National flag of the United States
Service Year
United States
National Origin

Ability to conduct aerial bombing of ground targets by way of (but not limited to) guns, bombs, missiles, rockets, and the like.
Equipped to search, track, and engage enemy underwater elements by way of specialized onboard equipment and weapons.
General transport functionality to move supplies/cargo or personnel (including wounded and VIP) over range.
Surveil ground targets / target areas to assess environmental threat levels, enemy strength, or enemy movement.

57.7 ft
(17.60 meters)
89.6 ft
(27.30 meters)
15.1 ft
(4.60 meters)
16,314 lb
(7,400 kilograms)
Empty Weight
27,778 lb
(12,600 kilograms)
Maximum Take-Off Weight
+11,464 lb
(+5,200 kg)
Weight Difference

2 x Wright R-1820-53 radial piston engines developing 1,000 horsepower each.
215 mph
(346 kph | 187 knots)
Max Speed
23,885 ft
(7,280 m | 5 miles)
2,113 miles
(3,400 km | 1,836 nm)
1,030 ft/min
(314 m/min)

MACH Regime (Sonic)
RANGES (MPH) Subsonic: <614mph | Transonic: 614-921 | Supersonic: 921-3836 | Hypersonic: 3836-7673 | Hi-Hypersonic: 7673-19180 | Reentry: >19030

1 x 0.30 caliber machine gun in nose position
1 x 0.30 caliber machine gun in dorsal position
1 x 0.30 caliber machine gun in ventral position

Up to 4,500lbs of internally-held ordnance (conventional drop bombs or depth charges).

2 x 0.50 caliber heavy machine guns in starboard installation (anti-submarine).


DB-1 - Single Example Prototype Model
B-18 - Initial Production Model; at least 131 examples produced (may be 133).
B-18M - Trainer Conversion Models based on B-18; sans bomb equipment.
DB-2 - Single Example Prototype; fitted with power-operated nose turret.
B-18A - Improved Base B-18 Models; fitted with Wright R-1820-53 series engines; relocated bombardier's position; 217 examples produced.
B-18AM - Trainer Conversion Models based on B-18A; sans bomb equipment.
B-18B - Anti-Submarine Warfare Model; 122 conversions completed.
B-18C - Anti-Submarine Warfare Model; 2 examples produced; forward-firing .50 caliber heavy machine guns; glassed-over lower nose.
XB-22 - Proposed Improved B-18; fitted with Wright R-2600-3 radial engines of 1,600 horsepower.
C-58 - Conversion Transport Model
Digby I - Modified Canadian B-18A Model

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