The Douglas Boston III was the most important version of that aircraft in RAF service, with a total of 768-771 aircraft produced. It was also the first British version to be actually be used as a bomber, and the first version to have come from the original British order for the Douglas DB-7B.
British interest in the DB-7 had started in 1939. After examining the DB-7A being produced for the French, the British Purchasing Commission in the United States began negotiations with Douglas to purchase an improved version of the aircraft.
While the French wanted the DB-7A for relatively short range bombing missions, the British needed an aircraft with longer range. The DB-7B could carry 394 US gallons of fuel, early twice the 205 gallons of the DB-7A, and was given better self-sealing fuel tanks that the French aircraft. The same 1,600hp Wright R-2600-A5B radial engines were used, so the heavier British aircraft had a slightly slower top speed than the French DB-7A.
The DB-7B was armed with six 0.303in machine guns. It was soon discovered that the four nose guns would not fit in the same space as their French equivalents, and so the DB-7B was given machine gun blisters just below and behind the glass nose. The British also requested a slightly longer nose with a straight edge to the glass windows, which improved visibility.
The Boston IIIs came from a variety of sources. 300 were the original British DB-7Bs. One was a replacement for a crashed DB-7A. 480 came from the French order for DB-73s, with production split equally between Boeing and Douglas. The RAF received 568-571 of the 781 aircraft, with 206 of the remaining aircraft being retained by the USAAF and the other 4-7 aircraft lost.
These aircraft were followed by 200 Boston IIIA, produced under lend-lease. Some at least of these aircraft were A-20Cs produced by Boeing, but others came from Douglas production. The Boston IIIA was powered by Wright R-2600-23 engines, with the change of designation indicating the use of US military engines rather than export engines. The Boston IIIA also had a different electrical system, individual exhaust stubs and an extended carburettor intake which came to the front of the engine cowling.
The standard Boston III was used as a day bomber, operating over occupied France from the spring of 1942, as part of the RAF’s policy of “leaning over the Channel”.
A number of special versions of the Boston III were produced. The Boston III (Intruder) had a gun pack with four 20mm cannon installed under the fuselage, and was used as a night intruder alongside the Havoc I (Intruder). The Boston III (Turbinlite) had a powerful searchlight installed in the nose, and was used alongside the Havoc I/ II (Turbinlite), supporting night fighters.
Engine: Wright R-2600-A5B Double Cyclone
Power: 1,600hp takeoff and at 1,000ft, 1,400hp at 10,000ft
Width: 61ft 4in
Length: 46ft 6in
Empty Weight: 12,200lb or 15,051lb !
Gross Weight: 19,750lb
Normal Take off weight: 20,320lb
Overload weight: 23,500lb
Maximum speed at sea level: 311mph
Maximum speed at 11,000ft: 320mph
Maximum speed at 12,500ft: 338mph
Cruising speed: 273mph
Ceiling: 24,500ft or 27,600ft
Climb Rate: 2,420ft/min
Range: 1,240 miles; 745 miles with 1,000lb bombs, 525 miles with 2,000lb bombs
Guns: 4 fixed 0.303in Browning machine guns in nose, two flexible 0.303in Browning machine guns in dorsal position, one flexible Vickers K 0.303in machine gun in ventral position
Bomb load - Maximum: 2,000lb made up of four 500lb bombs
Normal bomb load: 1,000lb, either two 500lb or four 250lb bombs