Staff Writer (Updated: 6/29/2016):
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.