Douglas DB-7/ A-20/ Havoc/ Boston - Introduction and Development

Very few aircraft attracted a wider range of designations than the Douglas DB-7/ A-20 Havoc/ P-70 Nighthawk/ Havoc night fighter/ Boston bomber. Developed as an attack class aircraft for the US Army Air Corps, it was first ordered by the French in February 1939, and used as a standard level bomber. French requirements led to the development of the DB-7, which was ordered by the Army Air Corps in the summer of 1939 before the prototype had made its first flight. It went on to serve as a night fighter, light to medium bomber and ground attack aircraft, was operated by the USAAF, the RAF and the Soviet Air Force, and fought in the Pacific, in North Africa, in Italy, in support of the D-Day landings and on the Eastern Front, even taking part in the battle of Stalingrad. 

The Bomber Contests

In the late 1930s, with the war clouds gathering around the world, the Army Air Corps issued a series of aircraft specifications. Each of these specifications resulted in the development of a series of competing designs, many of which resulted in production aircraft.

The attack bomber contest that produced the A-20 began late in 1937 when the Army invited companies to submit designs for an aircraft with a range of 1,200 miles, a speed of 200mph and a 1,200lb bomb load. The official specifications were dated 18 January 1938, and the deadline for submissions was in July 1938.

Four companies responded with designs – Bell, Douglas, Glenn L. Martin and Stearman. Bell dropped out when the Army asked all four companies to build a prototype at their own expense, and was replaced by North American. The prototypes had to be completed by 17 March 1939.

All four prototypes – the Martin Model 167, Stearman X-100, North American NA-40 and Douglas Model 7B – were built within months. Of these only the Stearman X-100 failed to reach production in some form.

The North American entry had originally been developed in response to a specification for a twin-engined medium bomber, issued early in 1936. North American had produced two designs – the underpowered NA-21 and the improved NA-39 (Army designation XB-21 Dragon) but had lost out to Douglas’s own DB-1, a bomber based on the DC-3 and which became the B-18 Bolo. The experience gained on this project helped North American in the design of their entry in the attack aircraft contest, the NA-40. This aircraft came close to winning the contest, but on 11 April the prototype was destroyed in a crash, eliminating it from the contest. One month earlier the Army has issued a request for a medium bomber. North American responded with the NA-62, a modified version of the NA-40, and the new design finally entered production as the B-25 Mitchell.

The Army Air Corps was not interested in the Glenn L. Martin Model 167, but a French Purchasing Commission was. As the Martin 167 A-3 or “Glenn” it took part in the fighting of May-June 1940, before entering RAF service as the Martin Maryland, which then led on to the Martin Baltimore. 

Douglas had been working on a design for a twin engined attack aircraft since the start of 1936. Their first effort was the Model 7A, designed by Jack Northrop and Ed Heinemann. The Model 7A was a shoulder-winged bomber, powered by Pratt & Whitney R-985 Wasp Jr engines, with a slim fuselage and carrying a crew of two. The Model 7A had a projected top speed of over 250mph.

When the Army issued its 1937 specifications Douglas moved on to the Model 7B (by now Northrop had left, leaving Heinemann as the main designer). The Model 7B kept the shoulder wings of the Model 7A, but replaced the Wasp Jrs with 1,100hp Pratt & Whitney R-1830 S3C3-G Twin Wasp radial engines, increasing the total available power from 900hp to 2,200hp. The fuselage was shorter but wider than on the eventual DB-7. The Model 7B was designed with interchangeable noses – a solid nose with six .30in and two .50in guns or a glass bombardier’s nose.

The Model 7B made its maiden flight on 26 October 1938, well ahead of the March 1939 deadline. This had led to the often-repeated statement that although Douglas won the design contest, they did not immediately win a production contract. In fact the Army evaluation of the aircraft entered in the contest did not begin until the spring of 1939. In March 1939 tests began at Wright Field on both the Martin Model 167 and the North American NA-40. The Model 7B was absent from these tests, having been destroyed in a crash earlier in the year, and was in the middle of an extensive redesign. Despite this, within three months of the tests beginning Douglas received an order for sixty three of the improved aircraft as the A-20, at least two months before the flight of the prototype DB-7.

The Model 7B had performed well in early test flights at Douglas’s own facility. In December 1938-January 1939 it was shown to the French Purchasing Commission, then criss-crossing America looking for military aircraft to fill a gap before more modern French designs entered production. On 23 January a French observer, Captain Maurice Chemidlan, was onboard the aircraft to see how well it handled on a single engine. Unfortunately that single engine failed. The prototype was destroyed in the resulting crash, the test pilot was killed and Captain Chemidlan seriously injured.

Despite this the French were still interested in buying the Douglas aircraft, and placed an order for 100 aircraft in February 1939. However, the French required a number of modifications to be made. They wanted more armour, longer range and a bigger bomb load, as well as the use of standard French equipment and weapons. Douglas agreed to produce the new design, and redesignated the aircraft again, this time as the DB-7 (Douglas Bomber No.7). The new aircraft did not make its first flight until 17 August 1939. By then Douglas were also working on the improved DB-7A for the French and DB-7B for the British.

In the meantime the March tests had not gone well. The Martin design had been rejected, and the North American NA-40 had been destroyed in the crash of 11 April. In June 1939 the Army Air Corps placed an order for 63 A-20s, similar in design to the RAF’s DB-7B. Douglas received their first American order for the A-20 two months before the prototype DB-7 made its first flight.

The DB-7

Plans of the Douglas A-20G Havoc
Plans of the Douglas A-20G Havoc

Compared to the Model 7B the DB-7 had a taller but narrower fuselage. This reduced drag and increased the space available for fuel tanks, but made it impossible for the crew to swap positions; so on early production aircraft the gunner was given a rudimentary set of controls. The wings were moved down from the shoulder position of the Model 7B to a mid-wing position (although it may be more accurate to say that the fuselage was expanded upwards above the wings). The engines nacelles were moved from their mid-wing position to below the wings, leaving the rear landing wheels at the same length. The nose wheel was made slightly longer, giving the DB-7 a slightly “nose-up” look when landed. The engine was changed again, to the R-1830-SC3-G.

The interchangeable noses of the Model 7B were replaced by a single nose with glass panels for the bombardier (with a distinctive stepped edge on the original DB-7 and DB-7A), with four machine guns mounted behind and below the glass. The rear guns were rather more limited – the single gunner could chose between a single dorsal gun in a manual mounting (protected by a sliding glass cover when not in use) or a single ventral gun in a tunnel position. All six guns of the original DB-7 were French 7.5mm Chatellerault machine guns.

The new aircraft made its maiden flight on 17 August 1939. The first production aircraft was completed in October 1939. In the same month that France ordered another 170 aircraft. This followed the June 1939 order for the first A-20s, and was soon followed by a February 1940 order for 150 DB-7Bs for the RAF.

The DB-7/ A-20/ Havoc/ Boston remained in production until 20 September 1944, and a total of 7,385 aircraft were built.

The biggest user of the A-20 was the Soviet Union, which received 3,125 aircraft, or 42% of the total production. Little is known about its use in Soviet hands, although more information is slowly emerging. It is known to have been used in large numbers as a ground attack aircraft during the battle of Stalingrad, and to have served as a torpedo bomber in the Black Sea and the Baltic.

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How to cite this article: Rickard, J (5 September 2008), Douglas DB-7/ A-20/ Havoc/ Boston – Introduction and Development , http://www.historyofwar.org/articles/weapons_douglas_db-7_a-20_havoc.html

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