Although the French Armee de l'Air was generally happy with the performance of the DB-7, they were curious to see if substantial performance enhancements could be obtained with larger, more powerful engines. On October 20, 1939, the French Purchasing Commission ordered a third batch of 200 aircraft from Douglas, the powerplant specified being the 1600 hp Wright R-2600-A5B Double Cyclone fourteen- cylinder air-cooled radial. This variant was designated DB-7A.
As it turned out, the DB-7A was basically the export version of the USAAC A-20A. Due to the use of more powerful engines, the nacelles were elongated and the rear portion of the nacelles had a longer and more pointed shape as compared to the nacelle of the DB-7. Cooling vents were added to the sides of the engine cowlings, and the R-2600 engines had a large exhaust on the outboard side of the nacelles. There was a fear that the extra power offered by the R-2600 engines might result in some directional instability, so the vertical fin and rudder were increased in size. Additional structural strength was provided in the tail area. The carburetor air scoop was relocated from the front edge of the cowling to behind it. In the original French specification, the DB-7A aircraft were to have had similar armament as the DB-7 but were to be equipped with a fixed, aft-firing machine gun mounted in the rear of each engine nacelle.
A twin tail configuration was tested on two aircraft to see if control and stability could be improved and to determine if the field of fire of the rear gunner could be enhanced. After some testing, it was found that the twin tail configuration offered no appreciable advantages, and the two aircraft reverted to standard single-tail configuration.
The first DB-7A flew in August of 1940. By this time, France had fallen and the DB-7A order had been taken over by the United Kingdom. All of the DB-7As were delivered to the Royal Air Force, where there were given the name Havoc II and assigned the serials AH430 to AH529. All but the first aircraft (AH430, which crashed during a test flight in the USA) were delivered to Britain. Before delivery, the aircraft were brought up to British standards, which included the replacement of French 7.5-mm machine guns by 0.303-inch guns and the replacement of French controls by British controls.
The DB-7A had a maximum weight of 16,700 pounds, and a maximum speed of 308 mph at sea level and 344 mph at 12,500 feet. This was substantial performance for the day, and only slightly slower than contemporary single-seat fighters of the day such as the Supermarine Spitfire Mk. 1 and the Messerschmit Bf 109E.
The Havoc IIs were all converted to night fighter configuration and fitted with a new Martin Baker-built unglazed nose housing twelve fixed forward-firing 0.303-inch Browning machine guns. They were painted with standard British day camouflage on top and side surfaces, but had their undersurfaces painted black. Before delivery to Britain, AH463 was experimentally fitted with a mockup of a Boulton Paul dorsal turret.
Thirty-nine Havoc IIs (among them serial numbers AH431, AH432, AH434, AH436, AH444 to AH447, AH450, AH451, AH453, AH460, AH468, AH470, AH472, AH473, AH478, AH479, AH481, AH483, AH484, AH491, AH497, and AH503) were later modified to carry 2700 million candlepower Turbinlite searchlights in their noses, and had all their armament deleted. The searchlights were powered by large and heavy batteries carried in the bomb bay. The theory of their operation involved their cooperation with Hurricane fighters. Ground radar would locate the enemy aircraft, and the Havoc II (Turbinlite) would illuminate the target aircraft so that it could be attacked by the Hurricanes. These Turbinlite Havoc IIs served briefly until the development of centimetric radar made such techniques obsolete. The ten operational squadrons which had been formed around the Havoc I and II were disbanded in early 1943.
The few DB-7As not converted to Havoc II configuration were designated Boston III, and were not distinguished from DB-7Bs, DB-73s and ex-USAAF A-20Cs which were also designated Boston III.
AH438, AH451, and AH454 were transferred to the USAAF.
Engines: Two Wright R-2600-A5B Double Cyclone fourteen-cylinder twin-row
air-cooled radials equipped with two-speed superchargers, rated at
1600 hp for takeoff and 1400 hp at 10,000 feet.
Performance: Maximum speed 344 mph at 12,500 feet. Cruising speed
275 mph. Initial climb rate 2420 feet per minute. Service ceiling
27,680 feet. 490 miles combat range.
Dimensions: Wingspan 61 feet 3 inches, length 47 feet 0 inches,
height 15 feet 10 inches, wing area 464 square feet.
Weights: 13,674 pounds empty, 19,322 pounds gross.
Armament: Four 7.5-mm machine guns paired in fairings on the side of
the fuselage. One 7.5-mm machine gun in flexible dorsal position.
One 7.5-mm machine gun in ventral tunnel position. One fixed
aft-firing 7.5-mm machine gun in the rear of each engine nacelle.
Maximum bomb load 1764 pounds.