Editing Consolidated B-24 Liberator (section)

===Prototypes and service evaluation===
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The U.S. Army Air Corps awarded a contract for the prototype XB-24 in March 1939, with the requirement that one example should be ready before the end of the year. Consolidated finished the prototype and had it ready for its first flight two days before the end of 1939. The design was simple in concept but, nevertheless, advanced for its time.
Consolidated incorporated innovative features such as a tricycle landing gear and Davis wing.

Compared to the B-17, the proposed Model 32 had a shorter fuselage and 25% less wing area, but had a {{convert|6|ft|m|abbr=on}} greater [[wingspan]] and a substantially larger carrying capacity, as well as a distinctive twin tail. Whereas the B-17 used 9-cylinder [[Wright R-1820]] Cyclone engines, the Consolidated design used twin-row, 14-cylinder [[Pratt & Whitney R-1830]] "Twin Wasp" radials of {{convert|1000|hp|kW|abbr=on}}. The maximum takeoff weight was one of the highest of the period.

The new design would be the first American heavy bomber in production to use tricycle landing gear – the [[North American B-25 Mitchell]] medium bomber's predecessor, the NA-40 introduced this feature in January 1939 – with the Consolidated Model 32 having long, thin wings with the efficient "Davis" high [[aspect ratio (wing)|aspect ratio]] design (also used on the projected Model 31 twin-engined commercial flying boat)<ref>Donald 1997, p. 266.</ref> promising to provide maximum [[fuel efficiency]]. Wind tunnel testing and experimental programs using an existing Consolidated Model 31 provided extensive data on the flight characteristics of the Davis airfoil.<ref>Birdsall 1968, p. 40.</ref>

Early orders, placed before the XB-24 had flown, included 36 for the USAAC, 120 for the [[French Air Force]] and 164 for the [[Royal Air Force]] (RAF). The name "Liberator" was originally given to it [[British military aircraft designation systems#Names|by the RAF]], and subsequently adopted by the [[United States Army Air Forces|USAAF]] as the official name for the Model 24.<ref name="Taylor 1968, p. 463">Taylor 1968, p. 463.</ref> When France fell in 1940, their aircraft were re-directed to the RAF. One outcome of the [[British Purchasing Commission|British and French purchasing commissions]] was a backlog of orders amounting to $680m, of which $400m was foreign orders, US official statistics indicating tooling, plant and expansion advanced the previously anticipated volume of US aircraft production by up to a year. A consequence of the British orders went beyond requests for specific modifications: as the RAF accepted some designs while rejecting others, American production was – to some extent – re-directed along specific lines that accorded with British doctrine, the B-24's capacious bomb bay and ability to carry 8,000&nbsp;lb ordnance a case in point.<ref name=":1" />

After initial testing, the '''XB-24''' was found to be deficient in several areas. One major failure of the prototype was that it failed to meet the top speed requirements specified in the contract. As built, the XB-24 top speed was only 273&nbsp;mph instead of the specified 311&nbsp;mph. As a result, the mechanically supercharged Pratt & Whitney R-1830-33s were replaced with the [[turbocharger|turbo-supercharged]] R-1830s. Additionally, the tail span was widened by {{convert|2|ft|m|abbr=on}} and the [[pitot-static system|pitot-static probes]] were relocated from the wings to the [[fuselage]]. The XB-24 was then re-designated XB-24B—these changes became standard on all B-24s built starting with the B-24C model.

[[File:YB-24.jpg|thumb|An early B-24D]]
In April 1939, the USAAC initially ordered seven '''YB-24''' under [[Consolidated Aircraft|CAC]] contract # 12464. The US policy at the time, despite neutrality, was that American requirements could be deferred while its Allies could immediately put US production into the war effort. The added advantage was the American types could be assessed in the European war zone earlier. Thus the first six YB-24 were released for direct purchase under CAC contract # F-677 on 9 November 1940. These aircraft were redesignated '''LB-30A'''. The seventh aircraft was used by Consolidated and the USAAC to test [[armor]] installations as well as [[self-sealing fuel tank]]s. Initially, these aircraft were to be given USAAC serials 39–681 to 39-687. Due to deferments of the US requirements, the US purchase was twice postponed, and the serial numbers were changed to 40–696 to 40-702. When the RAF purchased the first six YB-24 aircraft, the serial numbers were reassigned to an early batch of B-24D funded by the deferment.