Douglas DB-7 Boston / A-20 Havoc / P-70
In 1936 Douglas began its Model 7 as a light attack bomber as a private venture, produced to the order of the French government. After considerable refinement this flew on 26 October 1938 as the Model 7B private venture prototype with 1,100-hp (820-kW) Pratt & Whitney R-1830 radials. The type was maneuverable and fast, and soon elicited a French order for 100 somewhat revised DB-7s. The first production DB-7 flew on 17 August 1939. When France fell the undelivered aircraft outstanding from French contracts were taken over by the British government and given the name Boston. Only 60 were delivered, and 20 more passed to Great Britain.
Further French orders covered 100 DB-7As and 481 DB-7Bs. Most of these served with the Royal Air Force as Havoc Mk II night fighters and Boston Mk II bombers respectively. Later Bostons were patterned on A-20 aircraft for the US Army Air Forces, and served mainly over North-West Europe.
As delivered to the RAF from the French contracts, the Boston I was powered by two Pratt & Whitney R-1830-S3G-4G engines. It was used mainly for training duties, although some were converted for night fighting and given the British name Havoc. The A-20 was the first of the series built to a US Army specification and was powered by two 1,112kW Wright R-2600-7 Cyclone engines with exhaust-driven turbo-superchargers. It was fitted with American armament and equipment.
As the Boston II for the RAF, the A-20 had R-2600-A5B engines and British armament. Those converted into night fighters became Havocs each with a lengthened nose fitted with 12 forward-firing 7.62mm guns, AI radar and other special equipment depending on the sub-variant - one carried a high-power searchlight in the nose. As an intruder it carried a crew of three and full armament and bombs.
The observer (not only bomb aimer) was completely cut off from the pilot. Because of this the gunner had at the back a duplicate joystick. On high level operations a Vickers K gun was mounted in the rear entrance hatch. A camera was also carried mounted in this hatch.
It may be of interest that the very first operation carried out by the USA against Europe was on July 4, 1942, when six of their Bostons were led by six 226 Squadron Bostons.
The A-20A for the USAAC/USAAF was powered by two 1,192kW Wright R-2600-11 engines with integral two-speed superchargers. The A-20B was an experimental development of the A-20A, armed with two 12.7mm guns firing forward, one 12.7mm upper flexible gun, one 7.62mm lower flexible gun, and one 7.62mm gun in the tail of each engine nacelle, firing aft. Nacelle guns were remotely controlled by a foot trigger in the rear compartment. The A-20C was powered by two similarly rated R-2600-23 engines. Armament comprised four fixed guns (two on each side of the transparent nose), two on a flexible mounting in the rear cockpit, and one in the lower rear-firing position - all 7.62mm (A20G) or 7.69mm (British Boston Ill). Ejector-type exhaust stacks replaced the collector rings used on the earlier models and range was increased by the addition of a self-sealing fuel tank in the forward and rear bomb-bay compartments. Provision was also made on some aircraft to carry a 900kg naval torpedo.
Douglas A-20 Havocs, 1939
The Boston III was powered by R-2600-A5B engines and carried a crew of four as a bomber. The Boston IIIA was similar but built by Boeing. Some Boston III/IIIA were fitted as intruders with four 20mm cannon under the forward fuselage, four 7.69mm guns in the nose, and two 7.69mm guns in the upper flexible position.
Following the experimental XA-20E, with a 37mm nose cannon and General Electric turrets, the A-20G appeared. This was similar to the A-20C except that the transparent bombardier nose was replaced by a solid nose fitted (in earlier versions) with four 20mm cannon and two 12.7mm machine-guns and ultimately with six 12.7mm guns. A few also had a single 12.7mm upper flexible gun, but this was soon replaced by a power-driven turret armed with two 12.7mm guns. Thicker armour for increased crew protection on ground-attack missions was also added.
The A-20H was powered by two 1,267kW R-2600-29 engines and incorporated minor improvements. The A-20J was identical to the later version of the A-20G except that the attack nose was replaced by a moulded-plastic bombardier's nose incorporating bombing controls and flight navigation instruments. One in ten A-20G were completed as A-20J to serve as squadron lead planes. Armament consisted of two 12.7mm machine-guns (one in each side of the transparent nose), two in the power-operated dorsal turret and one in the lower rear firing position.
The A-20K was identical to the A-20H except that the attack nose was replaced by a bombardier's nose, as with the A-20J. The British Boston V was similar. Special US versions of the A-20 appeared as the P-70 night fighter with R-2600-11 engines and armed with four 20mm cannon mounted in a fairing beneath the fuselage bomb bay; the P-70A conversion of the A-20G with R-2600-23 engines and six 12.7mm machine-guns in a solid nose and dorsal and lower guns; the P-70B development of the P-70A for training, with six 12.7mm 'package' guns and special radar (converted A-20G/J); the F-3A night photographic-reconnaissance conversion of the A-20J/K; and BD-1/2 target tugs for the US Navy.
Production for the RAF, USAAF, US Navy and Russia ceased on 20 September 1944 after well over 7,000 had been built. Russia received twice as many as the RAF and only some 800 less than the US Army.
DB-7A (Wright R-2600, many passed to Great Britain as Havoc Mk Is)
DB-7B (revised systems and larger vertical tail)
Boston Mk I (taken-over DB-7s)
Boston Mk II (taken-over DB-7Bs converted to Havoc Mk I)
Boston Mk III (British DB-7Bs)
Boston Mk IIIA (200 Lend-Lease A-20Cs with British equip-ment)
Boston Mk IV (169 Lend-Lease A-20Js with heavier fixed armament)
Boston Mk V (90 Lend-Lease A-20Ks with more power).
P-70 version of the A-20 became an early night fighter.
DB-7B / Boston Mk III
Engines: two 1,500-hp (1,119-kW) Wright R-2600-A5B Cyclone radial
Maximum speed 311 mph (500 km/h) at sea level
Initial climb rate 2,000 ft (610 m) per minute
Service ceiling 25,170 ft (7,670 m)
Range 525 miles (845 km)
Empty weights: 15,051 lb (6,827 kg)
Maximum take-off 21,580 lb (9,790 kg)
Wingspan 61 ft 4 in (18.69 m)
Length 47 ft 3 in (14.40 m)
Height 18 ft 1 in (5.51 m)
Wing area 464.0 sq ft (43.11 sq.m)
Armament: seven 0.303-in (7.7-mm) machine guns, and up to 2,000 lb (907 kg) of bombs.
Engines: 2 x Wright R-2600-23 Cyclone 14, 1578 hp / 1193kW
Max take-off weight: 12338 kg / 27201 lb
Empty weight: 7250 kg / 15984 lb
Wingspan: 18.69 m / 61 ft 4 in
Length: 14.63 m / 47 ft 12 in
Height: 5.36 m / 17 ft 7 in
Wing area: 43.20 sq.m / 465.00 sq ft
Wing loading: 58.63 lb/sq.ft / 286.00 kg/sq.m
Max. speed: 275 kts / 510 km/h / 317 mph
Cruise speed: 200 kts / 370 km/h / 230 mph
Service ceiling : 25000 ft / 7620 m
Range: 891 nm / 1650 km / 1025 miles
Armament: 9 x 12.7mm 50 MG (12,7mm) machine-guns, 1800kg of bombs