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| Douglas DB-7B Boston III | ||
|---|---|---|
| Description | ||
| Role | Medium Bomber | |
| Crew | 3-4 | |
| First Flight | October 26, 1938 (Model 7B) | |
| Entered Service | ||
| Manufacturer | Douglas, Boeing | |
| Dimensions | ||
| Length | 47ft 4in | 14.4 m |
| Wingspan | 61ft 4in | 18.7 m |
| Height | 18ft 1in | 5.5 m |
| Wing Area | 464 ft² | 43.1 m² |
| Weights | ||
| Empty | 0 lbs | 0 kg |
| Loaded | 24,000 lbs | 10,880 kg |
| Maximum takeoff | lbs | kg |
| Powerplant | ||
| Engine | 2 × Wright Cyclone GR-2600-A5B | |
| Power (each) | 1,350 hp | 1,010 kW |
| Performance | ||
| Maximum speed | 350mph @ 12,000ft | 563km/h @ 3,660m |
| Combat range | 1,080 miles | 1,740 km |
| Ferry range | km | miles |
| Service ceiling | 23,600 ft | 7,190 m |
| Rate of climb | ft/min | m/min |
| Wing loading | 51.7 lb/ft² | 252.4 kg/m² |
| Power/Mass | 0.113 hp/lb | 0.186 kW/kg |
| Armament | ||
| Guns | 8 × 0.303 machine-guns | |
| Bombs | 2,000 lbs | 900 kg |
The Douglas A-20 series, Douglas model DB-7, was a family of bomber and fighter aircraft of World War II, serving with United States, British, Soviet, French and Australian services.
In March 1937 a design team headed by Donald Douglas, Jack Northrop and Ed Heinemann produced a proposal for a light bomber powered by a pair of 450hp (340kW) Pratt & Whitney R-985 Wasp Junior engines mounted on a high-mounted wing. It was estimated it could have carried 1000lb (450kg) bombload at 250mph (400km/h). Reports of aircraft performance from the Spanish Civil War indicated that this design would be seriously underpowered, and it was not progressed.
In the autumn of the same year, the Army Air Corps issued its own specification for an attack aircraft. The Douglas team, now headed by Heinemann, took the model 7A design, upgraded massively to 1100hp (820kW) Pratt & Whitney R-1830 S3C3-G Twin Wasp engines, and submitted the design as the Model 7B. It faced competition from the North American NA-40, the Stearman X-100, and the Martin 167F. The Model 7B was maneuverable and fast, but did not attract any US orders.
The model did, however, attract the attention of a French Purchasing Commission visiting the USA. The French participated in the flight trials, discretely so as not to attract criticism from US isolationists. The French ordered 100 production aircraft, which order was increased to 270 when the war began.
The French order called for substantial modifications, and the new designation DB-7 (for Douglas Bomber 7) was introduced. It had a narrower deeper fuselage, 1000hp (750kW) Pratt & Whitney R-1830-SC3-G radials, and French guns and metric instruments. Midway through the delivery, engines were switched to 1100 hp (820kW) Pratt & Whitney R-1830-S3C4-G. The French designation was DB-7 B-3 (the B-3 meaning "three-seat bomber").
The DB-7s were shipped in sections to Casablanca for assembly and service in France and French North Africa. When the Germans invaded France on May 10, 1940 the 64 available DB-7s were deployed against the advancing Panzers. Before the armistice they returned to North Africa, and some were used by Vichy French forces on the Axis side. A few were still operating under Free French colours to the end of the war in Europe.
The Royal Air Force agreed to take up the balance of the now-frustrated French order was diverted to Britain, and the aircraft were designated Boston Mk.I or Mk.II according to the earlier or later engine type.
The aircraft was not really suitable for RAF use as its range was too limited for day-time raids on Germany. Many of the Boston Mk.II, plus some re-engined Mk.Is, were converted for nighttime duties - either as intruders with 2,400lbs (1,100kg) bombs, or as night-fighters with AI Mk. IV radar. These were known collectively as Havoc Mk. I. 181 Bostons were converted to Havocs. Havoc Intruders caused considerable damage to German targets.
20 Havocs were Havoc Mk. I (Pandora) intruder aircraft, trailing the Long Aerial Mine (LAM) which was an explosive charge trailed on a long cable in the path of enemy aircraft in the hope of scoring a hit. It was not successful and they were converted back to Mk.I intruders.
A further 31 were Havoc Mk. I Turbinlite fitted with a 2700 million candlepower (2.7Gcd) searchlight in the nose. They were unarmed and were supposed to illuminate targets for accompanying Hurricanefighters, but in practice they just made nice bright targets for German gunners.
The French Purchasing Commission ordered a further 200 bombers, to be fitted with 1600hp (1190kW) Wright R-2600-A5B Double Cyclone engines. This variant was designated DB-7A by Douglas. None had been delivered before the fall of France, and they served instead as night-fighters with the RAF under the name of Havoc Mk.II. They had an impressive top speed of 344mph (550 km/h) at altitude. 39 of them were used briefly in Turbinlite roles.
The DB-7B was the first batch of the series to be actually ordered by Britain, in February 1940. Powered by the same engines as the DB-7A, with better armor and, crucially, larger fuel tanks, these were at last suitable for British use in the light bomber role. This was the batch for which the name Boston was first reserved, but since the commandeered DB-7s entered service first, this batch became known as Boston Mk.III. Amongst other operations they took part in the attacks on the Scharnhorst, Gneisenau and Prinz Eugen during their escape dash through the English Channel in February, 1942. 300 were delivered and some were used in Intruder and Turbinlite roles.
The DB-73 was a very similar design for France, which again were diverted to England as Boston Mk.IIIA. Many of these were built under licence by Boeing. Events further overtook this shipment after the German attack on the Soviet Union on June 22, 1941 and the Attack on Pearl Harbor on December 7, when many Bostons were sent to Russia and many more retained by the USAAF for its own use. Some 22 were also sent to the RAAF.
The DB-7C was a Netherlands order intended for service in the Netherlands East Indies, but the Japanese invasion was complete before they were delivered and they were sent instead to the Soviet Union under Lend-Lease.
The original American indifference to the Model 7B was overcome by the improvements made for the French and British, and the Army Air Corps ordered two models, the A-20 for high-altitude bombing and the A-20A for lower-altitude work. Both were similar to the DB-7B, the A-20 was to be fitted with turbosupercharged Wright R-2600-7 engines, but these were bulky and the prototype suffered cooling problems, so the remainder were completed with the un-supercharged R-2600-11, 59 as P-70 fighters and 3 as F-3 reconnaissance panes (of which more later).
The US Army ordered 123 A-20As with R-2600-3 engines, and a further 20 with more powerful R-2600-11. They entered service in spring, 1941. The Army liked the A-20A because of its excellent performance and because it had no adverse handling characteristics. 9 of them were transferred to Australia in 1943. The British name Havoc was adopted for the A-20A.
The A-20B received the first really large order - 999 - from the US Army. They resembled the DB-7A rather than the DB-7B, with light armor and stepped rather than slanted glazing in the nose. In fact, 665 were exported to the Soviets, so rather few actually served with the USAAC.
The A-20C was an attempt to standardize on a common British and American version, produced from 1941. It reverted to the slanting nose-glass and had RF-2600-23 engines, self-sealing fuel tanks and additional armor. They were equipped to carry an external 2000 lbs (900kg) naval torpedo. 948 were built for Britain and the Soviet Union, but many were retained by the USAAF after Pearl Harbor.
The A-20G, delivered from February 1943, would be the most produced of all the series - 2850 were built. The glazed nose was replaced by a solid nose contain four 20mm cannon and two 0.50in Colt-Browning machine guns, making the aircraft slightly longer than previous versions. After the first batch of 250 the unreliable cannon were replaced by more machine guns. Some had a wider fuselage to accommodate a power driven gun turret. Many A-20Gs were delivered to the Soviet Union. The powerplant was the 1600hp R-2600-23. US A-20Gs were used on low-level sorties in the New Guinea theatre.
The A-20H was the same continued with the 1700hp (1270kW) R-2600-29. 412 of these were built. The take-off weight was raised to 24,170lbs (10,960 kg).
The A-20J carried an additional bombardier in an extended plexiglass nose section. These were intended to lead bombing formations, with the following standard A-20s dropping their bombs when signalled by the leader. 450 were built, 169 for the RAF which designated them Boston Mk. IV from summer 1944.
The A-20K (Boston Mk. V in RAF parlance) was the final production version of the A-20 series, the same as the A-20J except for R-2600-29s instead of -23s.
In October 1940 the USAAC felt a need for long-range fighters more than attack bombers, so most of the production run of A-20s were converted to P-70 night-fighters. They were equipped with British AI Mk. IV radar, the glazed nose often painted black to reduce glare, and had four 20mm cannon. Further P-70 variants were produced from A-20C G and J variants, later models having American centimetric radar fitted.
The F-3A was a conversion of 46 A-20J and K models for night-time photographic reconnaissance (F-3 were a few conversions of the original A-20).
When A-20 series production finally ended on September 20, 1944, a total of 7098 had been built by Douglas and a further 380 by Boeing.
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