The Douglas DB-7/A-20 Boston/Havoc was one of the most popular and effective light bombers of the Second World War. A total of 7478 of these bombers were built, and they served with the French Armee de l'Air under the designation DB-7, with the USAAF under the designation A-20, and with the RAF, RAAF, and SAAF under the designation Boston. However, the largest single user of the Boston/Havoc was actually the Soviet Union, with over 3000 of the 7478 built being sent to the Russian ally during the Second World War. Although it never achieved the degree of public fame attained by some of its contemporaries, it was one of the most important types of twin-engined light bombers of the Second World War, and was operated by American, Australian, Brazilian, British, Canadian, Dutch, French, Russian, and South African crews. It had a good performance and had excellent handling characteristics. It had many features which could be considered as being advanced for its time such as a tricycle undercarriage and a two-compartment bomb bay.
The origin of the DB-7/A-20/Havoc/Boston series can be traced back to March of 1936, when Donald Douglas, Jack Northrop, and Ed Heinemann and a group of Wright Field technicians drew up a set of requirements for a twin-engined light attack bomber. The initial work was carried out as a company-funded project at the Northrop Corporation of El Segundo, Ca., which was at that time 51 percent owned by Douglas. The proposal bore the designation Model 7A, and was a two-seater powered by a pair of 450 hp Pratt & Whitney R-985 Wasp Junior nine-cylinder air-cooled engines housed in nacelles on a shoulder-mounted wing. The aircraft was very slim and had tricycle landing gear. Provisions were made for a number of flexible and fixed 0.30-inch machine guns to be carried and a light bomb load of up to 40 17-lb fragemtation bombs. As an alternative, a glazed lower mid-section reconnaissance or observation platform could be fitted in place of the bomb bay. A single fixed 0.30-inch machine gun was to be fitted in the nose firing forward, a single 0.30-inch gun was fitted in a manually-operated dorsal turret, and another 0.30-inch gun was installed in a dowarward-firing dorsal station. A bomb load of 1000 pounds could be carried. It was estimated that the Model 7A would have a maximum weight of 9500 pounds and would be capable of achieving a maximum speed of 250 mph.
The Model 7A project was set up by John Northrop with Edward Heinemann as the designer. However, by the time that the design was about half complete and a mockup had been built, combat information coming in from the Spanish Civil War indicated that the Model 7A would probably be obsolete even before it flew. The project was shelved in December of 1936. In the autumn of 1937, the Army issued its own set of requirements for a twin-engined light attack aircraft. The Army was interested in an aircraft that had a range of 1200 miles, a speed of 200 mph and a 1200-pound bombload. In late 1937, the Army invited companies to submit designs for such an aircraft, with the stipulation that proposals being ready for submission by July of 1938.
On January 1, 1938, Jack Northrop left the Douglas subsidiary that had previously borne his name to strike out on his own, and Ed Heinemann took over as chief designer on the attack bomber project. The design team used the Model 7A as a starting point, but it had to provide more speed, carry more armament, and be able to carry more bombs. The engines were now a pair of 1100 hp Pratt & Whitney R-1830 S3C3-G Twin Wasp fourteen-cylinder air-cooled radials, offering almost three times the available horsepower of the R-985s. Maximum weight was estimated at 15,000 pounds. Alternative nose sections were proposed, one being transparent for a bombardier position, and the other being solid and carrying a battery of six 0.30-inch and two 0.50-inch machine guns guns. The "transparent" nose model could also carry "blister" gun packs on either side of the nose. A single 0.30-inch machine gun could be housed in a retractable "birdcage"-type dorsal turret. A second 0.30-inch machine gun could fire downwards through an opening in the floor. A 2000 pound bombload was anticipated. The new design was designated Model 7B by the company.
The competitors of the Douglas Model 7B were the North American NA-40, the Stearman X-100, the Martin Model 167F, and the Bell Model 9. The Army invited all of the contestants to build prototypes of their designs at their own expense for a design competition. The deadline for the entries would be March 17, 1939. Bell backed out of the competition, but all of the other contestants submitted entries.
The Model 7B made its first flight on October 26, 1938. Powered by a pair of 1100 hp Pratt & Whitney R-1830 Twin Wasp engines, the Model 7B featured a shoulder-mounted wing and a slim fuselage. There were two crewmen--a pilot and a rear gunner. The rear gunner was provided with a retractable manually-operated dorsal turret carrying a single 0.30-inch machine gun. In addition, the rear gunner was provided with a single ventral gun which could fire through an opening in the floor at targets coming from below. The Model 7B featured interchangeable noses--a transparent "bomber" nose with a position for a bombardier and his associated equipment for low level missions and a solid "attack" nose fitted with six 0.30-inch machine guns and two 0.50-inch machine guns. When fitted with the "bomber" nose, teardrop-shaped blisters carrying a pair of 0.30-inch machine guns could be installed on the fuselage sides below the cockpit.
The Model 7B was maneuverable, fast, and had no serious handling vices. It flew with both the "solid" and "bombardier" noses during its brief career, and the only modification required as a result of flight testing was the moving of the horizontal tail surfaces forward and giving them some dihedral. Nevertheless, the US government made no attempt to acquire the aircraft.
However, it just so happened that the first flight of the Model 7B coincided with the arrival in the USA of the French Purchasing Commission which was seeking aircraft for the modernization of the Armee de l'Air in the wake of the Munich Crisis. The commission obtained US government permission to witness performance trials of the Model 7B, although this had to be kept secret so as not to raise any diplomatic problems or to arouse the suspicion of isolationist forces who were at that time quite strong in the USA.
Impressed by what they saw, the French Purchasing Commission asked for and received permission to participate in the flight trials. Throughout December of 1938 and into January of 1939, members of the commission took part in flight tests of the Model 7B. However, on January 23, 1939, while demonstrating single-engine handling capabilities, an engine failure caused the Model 7B to go into a tight spin at low altitude. The Douglas test pilot, John Cable was able to bail out, but his chute opened too late and he was killed. The French observer, Captain Maurice Chemidlin, was trapped in the spinning aircraft but managed to survive the crash, although with serious injuries. Unfortunately, the press found out about the presence of the French observer on the crashed Model 7B, and there was a firestorm of controversy in the media, with isolationist forces maintaining a constant drumbeat of criticism. There were repeated calls for the resignation of General Henry H. "Hap" Arnold, and he was under tight scrutiny for the next year. Things got so bad that President Franklin Roosevelt was forced to take personal blame for the incident, and apologized to the nation.
Although the crash of the Model 7B was a setback, the French Purchasing Commission was sufficiently impressed by the Model 7B that they ordered one hundred examples on February 15, 1939. This was the first solid order for the Douglas design, since the USAAC had yet to place any firm order. 170 more examples were added to the order in October, following the outbreak of war in Europe.
Engines: Two Pratt & Whitney R-1830 S3C3-G Twin Wasp fourteen-cylinder
air-cooled radials, each rated at 1100 hp at 5000 feet.
Performance: Maximum speed 304 mph at 5000 feet. Cruising speed 185
mph. Service ceiling 27,600 feet. Combat range 1555 miles
Dimensions: Wingspan 61 feet 0 inches, length 45 feet 5 inches, wing
area 464 square feet.
Weights: 15,200 pounds gross.
Armament: Solid "attack" nose: with six 0.30-inch machine guns and
two 0.50-inch machine guns. Transparent "bomber" nose: Four
0.30-inch machine guns paired in blisters located on the fuselage
sides below the cockpit. One flexible 0.30-inch machine gun in
retractable dorsal position, one flexible 0.30-inch machine gun in
retractable ventral position. Maximum bomb load 2000 pounds.