Douglas Boston Mk.I/Mk.II twin-engine medium army bomber/heavy ground-attack aircraft (second batch of the French order for the DB-7), series 1939
After it ordered the first batch of DB-7s, the French government finalized a new contract with the Douglas Aircraft Company for 170 more planes. These machines differed from the first batch by being equipped with Pratt & Whitney R-1830-S3C4-G fourteen-cylinder, double-row, radial air-cooled engines with two-speed superchargers that delivered better performance characteristics at higher altitudes, thus increasing their maximum speed. The maximum power of the new engines was raised to 1,200 hp.
Those aircraft that had not been sent from the USA before France was defeated were "inherited" by the British. The RAF gave the DB-7 its own service name, "Boston", to indicate its American origin.
The British had to alter the aircraft they had received. The instruments, which had been set to the metric system, were replaced. Throttle quadrants made according to the French standard were redone, and British radio sets and oxygen equipment were installed on the planes.
The defensive armament was also replaced with British armament. The forward fuselage now had four 7.7 mm Colt-Browning .303 Mk.II machine guns with 500 rounds each, fed by a disintegrating belt held in an ammunition box. The radio operator/gunner's cockpit had two 7.7 mm Vickers K machine guns with pan magazines and 470 rounds each; the first was located in the rear upper gun position, and the second in the lower hatch.
The DB-7 with Pratt & Whitney R-1830-SC3-G engines was designated the Boston Mk.I in the RAF, and the aircraft with Pratt & Whitney R-1830-S3C4-G engines was named the Boston Mk.II.
According to British pilots, the Boston had excellent controllability and good visibility from the cockpit. The aircraft's tricycle landing gear made takeoff and landing significantly easier.
The British did not want to use the DB-7s which the French had ordered as bombers due to their limited range, which prevented them from reaching German territory. A different application was found for these aircraft: they were converted into heavy night fighters. In addition, some planes were used for training and auxiliary purposes.
A total of 131 machines from the second batch of DB-7s ordered by France were transferred to the RAF.