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Boeing B-17 Flying Fortress (USA) Frustrated in their efforts to acquire a fleet of strategic bombers for service with the Army Air Corps, US Army planners - who were big devotees of the theories expounded by Brig Gen William 'Billy' Mitchell - insterted the thin end of an important wedge when they ordered a small number of YB-17 prototypes on January 1936, ostensibly for the nation's defence. Originating as the Boeing Model 299, the prototype was built as a private venture, Boeing gambling heavily on producing a winner that would bring a large military contract. It must have seemed to Boeing that their gamble had failed when, almost at the end of the military trials, the Model 299 crashed on take-off. Fortunately investigation proved that the aircraft had been flown off with the flying controls locked and safety of the basic design was not suspect.

It was not until 1938 that the USAAC was able to place an order for 39 production B-17Bs, the last of this batch entering service in March 1940. These were the first B-17 production aircraft to be equipped with turbocharged engines, providing a higher maximum speed and much increased service ceiling. Of the B-17s which followed, a batch of 20 were supplied to the RAF (designated Fortress I) and used operationally in Europe for evaluation, leading to improved B-17D and B-17E aircraft with self-sealing fuel tanks and revised armour and armament.

  The B-17E was truly a flying fortress, armed with one 0.30 in and 12 0.50 in machine-guns for defence and able to carry a maximum 7,983 kg (17,600 lb) of bombs. Most extensively built variant was the B-17G (8,680), being built by Douglas and Lockheed Vega as well as aat the Boeing plant, Seattle. Pratt & Whitney R-1820-97 radial engines and improved turbochargers enabled the B-17G to operate at an altitude of up to 10,670 m (35,000 ft); and the addition of a chin turret below the nose (containing two 0.50 in machine-guns) provided better defence against the head-on attacks being launched by Luftwaffe fighter pilots in their attempts to reduce the numbers of Fortresses striking daily at strategic targets deep in German territory.

Special variants included the B-40 with up to 30 machine-guns/cannons, which was intended as a B-17 escort, but proved to be an operational failure; BQ-7 pilotless aircraft packed with explosives to be deployed against German targets by radio control, which failed due to unreliable controll equipment; CB017 and C-108 transports; and F-9 long-range B-17 equipped to serve as an air-sea rescue aircraft and able to deploy a lifeboat carried beneath the fuselage.

In Britain, more than anywhere else in the world, the B-17 evokes vivid memories of courageous aircrew who day after day - despite sometimes horrific losses - continued to attack targets in Europe until victory was won. For Boeing, their private-venture gamble paid off: a total of 12,731 Fortresses were built by the Boeing, Douglas and Lockheed team.

Data (B-17G): Engines four 894 kW (1,200 hp) Pratt & Whitney R-1820-97 radials Wing span 31.62m (103 ft 9 in) Length 22.66 m (74 ft 4 in) Max T-O weight 29,710 kg (65,500 lb) Max level speed 462 km/h (287 mph) Range 3,219 km (2,000 miles) Armament 13 X 0.50 in machine-guns, plus bombs

Consolidated B-24 Liberator (USA) When in 1939 Consolidated Aircraft Corporation began design of a bomber aircraft intended to be superior to the Boeing B-17, the company could never have imangined that more than 18,000 of these aircraft would be built (as the B-24A to -M for the USAAF and Liberator I to IX for RAF Coastal Command and Bomber Command). The aim of the design team was to achieve better load/range performance than that of the B-17, the basis of the design being a wide-span narrow-chord cantilever wing, mounted high on a deep-section fuselage.

Construction was conventional all-metal, but there were several innovations in addition to the new wing. For the first time on a large aircraft a retractable tricycle-type landing gear was introduced. The bomb bay was deep enough for bombs to be stowed vertically and wide enough to comprise two bays separated by a catwalk providing communication between the flight deck and rear fuselage. Instead of conventional bomb doors, which can affect flight characteristics when open, the bomb bay was closed by roller-shutter-type doors.

The prototype XB-24 flew for the first time on 29 December 1939, by which time the USAAC had ordered seven YB-24s for service trials and others had been ordered by Great Britain and France. These had the same engines as the prototype, but introduced pneumatic de-icing boots for wing and tail unit leading edges. The first production B-24s were delivered in 1941 to the USAAF (and others to Britain as LB-30A transports for transatlanticferry flights). During the period of their construction the original prototype was re-engined with turbocharged Pratt & Whitney R-1830-41s, as the same time having the oil coolers mounted on each side of the engine.  This was responsible for the unusual elliptical cowlings which, together with the large twin oval endplate fins, made the Liberator easily identifiable.

Subsequent Liberators had increased armament and armour protection. The first major production version was the B-24D, powered by R-1830-43 engines, of which the majority of more than 2,700 built went to the USAAF as bombers. A number were subsequently taken over by the US Navy as PB4Y-1 anti-submarine aircraft. RAF Bomber Command and Coastal Command also received 382 as Liberator III/IIIAs and Vs. The major production version of the Liberator was, however, the B-24J with R-1830-65 engines, making up more than one-third of the total production. These were supplied to the US, British, Canadian and other air forces.

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Although the B-24 was deployed alongside the B-17 in Europe, and flew in Africa and the Middle East, its major contribution to America's wartime operations was in the Pacific, where it was first flown in action against the Japanese in January 1942. In Europe it is best remembered for bombing Rome on 19 July 1943 and for a low-level attack by 177 aircraft on the Ploesti oil refineries in Romania on 1 August 1943, a 4,345 km (2,700 mile) round-trip mission from Benghazi, Libya, during which 57 of these eight-ten-crew aircraft were lost. (See also Consolidated C-87 and PB4Y-2 Privateer)

Data (B-24M): Engines four 894 kW (1,200 hp) Pratt & Whitney R-1830-65 radials Wing span 33.53 m (110 ft 0 in) Length 20.47 m (67 ft 2 in) Max T-O weight 29,257 kg (64,500 lb) Max level speed 483 km/h (300 mph) Combat range 3,380 mkm (2,100 miles) Armament ten 0.50 in machine-guns, plus up to 3,992 kg (8,800 lb) bombs

Boeing B-29 Superfortress (USA) Some three years after the first flight of its model 299 prototype (subsequently designated B-17 Flying Fortress) Boeing approached the USAAC with proposals for an improved version of the B-17. The time was not yet ripe, however, for the Army had then (in 1938) only recently been permitted to place an initial contract for the 39 B-17Bs. However information on changing requirements in relation to operational needs allowed Boeing to keep updated their design, so that at the beginning of 1940, when the USAAF invited proposals for a long-range medium bomber, much of their basic thinking had already been done. The Boeing design (in competition with submissions from Consolidated, Douglas and Lockheed) was sufficiently interesting for three XB-20 prototypes plus a static test airframe to be ordered on 24 August 1940. Consolidated also received an order for three prototypes, their submission being built as the B-32 Dominator.

To provide better conditions for the crew of the B-29 Superfortress (as this aircraft became designated) three pressurised compartments were provided: one for the flight deck which accomodated the pilots, bombardier and flight engineer, connected via a tunnel above the bomb bays to the midships compartment for the observers and gunners; a separate pressurised section was provided for the tail gunner. Armament comprised ten or eleven guns in five turrets, of which four were remotely controlled and sigted from adjacent astrodomes. Because of what was considered to be a very high wing loading (initially 349 kg/m [[squared]], 171 lb/sq ft) Boeing developed a special wing aerofoil section and used Fowler-type flaps to provide satisfactory take-off and landing characteristics.

Deliveries of the first production B-29s began in the autumn of 1943; but it was not until 5 June 1944 that they were used operationally in an attack on Bangkok, followed ten days later by an attack on the Japanese mainland. These initial missions were launched from bases in India; the first B-29 operations from the Mariana Islands began in late November 1944. Maj Gen Curtis LeMay was selected to command the B-29 attacks on Japan in January 1945 and in March initiated low-level incendiary raids by night. These, between 10 and 20 March, destroyed about 83 km [[squared]] (32 sq miles) of the nations's four most important cities. Finally, on 6 and 9 August, the B-29s Enola Gay and Bock's Car dropped the world's only two operational atomic bombs on the Japanese cities of Hiroshima and Nagasaki, bringing World War II to an end shortly afterwards. Post-war a total of 88 B-29s served with the RAF as Washington B.Is, and the type continued in USAF service as flight-refuelling tankers and for air-sea rescue, photo-reconnaissance and weather reconnaissance.

A developed version of the B-29 with Pratt & Whitney R-4360 Wasp Major engines was built as the XB-44. When ordered into production it was designated B-50 and introduced a number of improvements. The first B-50A flew on 25 June 1947. B-50Bs had increased gross weight; B-50Ds additional fuel capacity; and conversion programmes produced KB-50 tankers, TB-50 trainers and WB-50 weather reconnaissance aircraft

Data (B-29A): Engines four 1,639 kW (2,200 hp) Wright R-3350 radials Wing span 43.05 m (141 ft 3 in) Length 30.18 (99 ft 0 in) Max T-O weight 64,000 kg (141,100 lb) Max level speed 576 km/h (358 mph) Range 6,598 km (4,100 miles) Armament 11 X 0.50 in machine0guns or ten 0.50 in guns and one 20 mm cannon, plus up to 9,072 kg (20,000 lb) of bombs

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