Boston III over Los Angeles, 1941
The negotiations between the British Purchasing Commission (BPC) and the Douglas Aircraft Company for the purchase of A-20-equivalent DB-7s began in December 1939, reflecting a significant interest by the British in supplementing their domestic aircraft production with modern American military planes. This interest stemmed from an earlier evaluation in 1938, where the British Air Commission found American combat aircraft wanting compared to European designs, resulting in no tactical aircraft contracts being placed that year. However, they did purchase 200 North American NA16 Harvards and 200 Lockheed 14 Hudsons as combat trainers.
Douglas, feeling slighted by the contracts awarded to North American and Lockheed, maintained strained relations with the British for several years. The establishment of the BPC in New York in November 1939 was a significant step towards improving these relations and securing new contracts. In December 1939, a joint meeting between the British and French Purchasing Commissions and US government officials, including President Roosevelt, discussed purchasing 8,400 aircraft, 13,650 engines, and 14,000 propellers.
On 23 December 1939, Douglas and the BPC announced discussions for a $40 million contract to purchase improved DB-7s. The initial specifications, designated DS-339, were based on the Air Corps A-20A, with modifications like British standard bomb racks and bombs, a 24-volt two-wire electrical system (eventually rejected), and changes to accommodate British bomb sizes and configurations. The DB-7B variant was largely based on the A-20A and powered by the Wright GR2600A5B engine.
Negotiations and design modifications took place in Santa Monica, New York, and London, with a contract signed on 20 February 1940 for 150 DB-7Bs. Initial specifications included a range of 1,150 miles, a cruise speed of 191 mph, and a maximum speed of 335 mph at 13,900 feet. Modifications during the negotiations included changes to the bomb-door actuating mechanism, fuel tank capacity, fixed gun mounts, and cockpit switch configurations.
Production of the DB-7Bs began in early January 1940, initially for 100 planes, increased to 150 by mid-January, and finally doubled to 300 aircraft on 17 April 1940. The first DB-7B flight was on 10 January 1941, with deliveries starting in April 1941 and completed by September 1941. The aircraft were designated as Boston III by the RAF, with serial numbers W8252 to W8401 for the first series and Z2155 to Z2304 for the second. The planes were delivered fully painted in RAF camouflage schemes, following specific finish specifications (FS-15) initially involving alternating patterns, later unified into a single scheme. The DB-7Bs were ferried to New York, disassembled, and shipped to Britain via British freighters.