Just as the Handley Page Halifax was overshadowed in the UK by its partner, the Avro Lancaster, so the B-24 never gained the popular appeal of its USAAF partner, the Boeing B-17. In fact, the B-24 was newer, more efficient, built in far greater numbers and, unlike the B-17, served on every front in World War II.
More effort, more aluminium and more aircrew went into the Liberator than into any other flying machine ever built. Nothing better underlines American industrial might than the fact that the prototype Liberator did not even fly until after the beginning of World War II, and the last (except for the PB4Y-2 model) came off the assembly line before the end of the war; yet, in between, deliveries of some 15 major variants totaled 18,188, or 19,203 including spares. This compares with 12,731 B-17s and 7,366 Lancasters.
The accomplishments of the Liberator were in proportion to its astronomic quantities; and, particularly in the matter of range, which to some degree stemmed from its having an unusually efficient wing, the Liberator gave the Allies capabilities they would not otherwise have possessed. Early in the war the first Liberators, in RAF markings, were the first aircraft in history to make North Atlantic crossings a matter of everyday routine. In 1942 a more developed version at last closed the gap in the western North Atlantic where U-boats had been able to operate beyond the range of other RAF aircraft. On countless occasions Liberator formations made attacks on targets that could be reached by no other Allied bomber until the advent of the B-29. Although primarily a heavy bomber, the Liberator was also a very effective fighter (in that it shot down something like 2,600 enemy aircraft), the leading Allied oceanic patrol and anti-submarine aircraft, and the leading Allied long-range cargo transport.
A demanding aircraft
At the same time it was a complicated and advanced machine, leading to prolonged pilot training programs and on occasion to severe attrition. Not only was it demanding to fly, even to a pilot fully qualified on the type, but it was eventually cleared to operate at such high weights that take-offs became marginal even with full power on all engines. Flight stability was also marginal, and escape from a stricken machine was extremely difficult once the pilot or pilots had let go of the controls. Moreover, though more modern and in most ways more efficient than the B-17, the overloaded late-model B-24s were hardly any improvement over their more primitive partners, and several commanders, including ‘Jimmy’ Doolittle, famed commanding general of the 8th Air Force, preferred the old B-17.
In fact, the B-24s might have been B-17s, because in October 1938 Consolidated Aircraft Corporation was asked if it would set up a second-source production line of the Boeing bomber. Consolidated had moved just three years earlier from icy Buffalo in New York state to sunny San Diego in California, and was well placed to expand its large new plant. But chief engineer Isaac M. ‘Mac’ Laddon had already made studies for long-range bombers and was confident of producing a superior design. Part of this confidence rested on the wing patented by David R. Davis: this had a particularly deep section, with sharp camber and a reflex curve on the underside, and was almost as slender as the wing of a sailplane. Tunnel tests confirmed Davis’s claim that this wing offered from 10 to 25 per cent less drag than ordinary wings, but no full-scale wing had flown. Laddon had designed a giant flying-boat, the Model 31, and this was to fly in spring 1939 with a Davis wing. Pending its measured drag figures he quickly drew a heavy bomber with the same wing and tail but a new fuselage with a futuristic smooth nose and tricycle landing gear. Under the mid/high-mounted wing were two bomb bays, each as large as that of a B-17.
The commanding general of the US Army Air Corps, H. H. ‘Hap’ Arnold, studied the plans of the Model 32 in January 1939 and told Laddon to go ahead, and “build a bomber that will fly the skin off any rivals.” Consolidated received a contract for the Model 32, designated XB-24, on 30 March 1939. It was to be able to reach 300 mph (483 km/h), 35,000 ft (10670 m) and 3,000 miles (4828 km). The Model 31 flying-boat flew on 5 May 1939, and met the promised drag figures. Design of the Model 32 went ahead quickly, although it was drastically altered to have a conventional nose with the navigator and bombardier in the front and a side-by-side cockpit further back with a stepped windscreen. The first XB-24 (US Army serial 39-680) made a successful flight from Lindbergh Field on 29 December 1939.
In through the bomb bay
This prototype was modern and impressive rather than beautiful, with a deep and stumpy fuselage and very large oval fins and rudders contrasting with the graceful wing. The engines were 1,100-hp (821-kW) Pratt & Whitney R-1830-33 Twin Wasps with geared superchargers, though it was planned to fit turbo superchargers later to increase the speed from the achieved 273 mph (439 km/h) to beyond the contractual figure. Each of the bomb bays could carry 4,000 lb (1814 kg) of bombs, with a catwalk down the centre to provide structural strength and crew access to the rear fuselage. To enter the aircraft the usual drill was to flick a small hydraulic lever on the right side of the bay. This opened the bomb doors, which rolled up the outside of the fuselage like a roll-top desk, the moving sections driven by large sprockets working directly on the corrugated inner stiffening skins. Then the crew of seven climbed onto the catwalk, the pilots, navigator, bombardier and radio operator going forwards and three gunners aft. Armament comprised five hand-held machine guns. Apart from the general complexity of the systems, and the extremely advanced Minneapolis-Honeywell autopilot, features included 12 flexible fuel cells in the wing, Fowler flaps and unusual main gears comprising single legs curved round the outside of single very large wheels which retracted hydraulically outwards to lie flat in the wing, where the wheel projected below the undersurface and needed a fairing.
In March 1939 the US Army Air Corps ordered seven YB-24s, and these were delivered in 1940 with additional fuel and equipment and pneumatic de-icer boots, but without fixed outer-wing slots. Only a month later, in April 1939, the French ordered 175 Model 32s in a version designated 32B7, but that country collapsed before delivery and the UK took on this contract, while ordering 165 on its own account. Of the 165, 25 were retained by the US Army and eventually 139 were delivered to the RAF as the LB-30 (Liberator British type 30), with the British designation Liberator Mk II. These were developed to British requirements and had self-sealing tanks, ample armour, R-1830-S3C4G engines driving Curtiss instead of Hamilton propellers, a lengthened nose, and completely re-thought equipment including 11 0.303-in (7.7-mm) Browning guns, eight of them in mid-upper and tail Boulton Paul electric turrets. Serial numbers began at AL503. The second LB-30 was completed as the unique VIP personal transport of Prime Minister Churchill, with the name ‘Commando’, unpainted bright finish and (in 1943) the tall single fin also used on the US Navy RY-3 transport and PB4Y-2 (its designation was Liberator C.Mk IX).
In parallel, Consolidated delivered the French order, converted from metric to RAF instruments and gear and known as the LB-30MF. RAF serial numbers of these began at AM258, and the basic designation was Liberator Mk I. Deliveries began in March 1941 and these aircraft served in many roles, including crew training, military transport, Atfero (Atlantic Return Ferry Service) transport between Prestwick and Montreal, civil BOAC services (joint RAF serials and civil registration) mainly on the route around Europe to Egypt, and with Coastal Command on long-range patrol, some aircraft having a belly installation of four 20-mm cannon firing ahead in addition to normal ASW weapons and ASV Mk I radar. The much better Mk II Liberators also served with Coastal Command but were employed mainly as bombers in the Middle East and India.
Thus all early deliveries went to the UK, but the US Army Air Corps (US Army Air Force from June 1941) received nine (of an order for 36) B-24As which introduced hand-held 12.7-mm (0.5-in) guns but retained Dash-33 engines. The turbocharged Dash-41 engine first flew on the original prototype in late 1940 in characteristic new cowlings of flattened oval shape, with the air ducts and oil coolers along the sides and the exhaust piped to the turbocharger on the underside of the nacelle under the wing. To absorb the power at high altitude, paddle-bladed propellers were fitted (invariably a Hamilton of 11 ft 7/3.53 m in diameter, with no spinner). As modified, the prototype became the XB-24B, other changes including self-sealing tanks and armour. These changes were all incorporated in nine B-24Cs (ordered as B-24As) delivered in 1941, which also had two American power turrets, a Consolidated in the tail and a Martin just aft of the cockpit, each with two 0.5-in (12.7-mm) guns, as well as three hand-held 0.5-in (12.7-mm) guns in the nose and waist positions.
Production on a vast scale
The B-24C was the basis of the first mass-produced variant, the B-24D, which had Dash-43 engines, two further nose guns plus a tunnel ventral gun (10 0.5-in/12.7-mm guns in all), increased outer wing tanks and a bomb load of 8,800 lb (3992 kg), or as an overload with reduced fuel eight 1,600-lb (726-kg) bombs (total 12,600 lb/5806 kg). From the start the B-24D was cleared to 56,000 lb (25402 kg) and by mid-1942 it was operating at 60,000 lb (27216 kg), making it the heaviest aircraft in production in the USA (the Halifax and Lancaster had just been cleared to the same weight) . Plans were rushed ahead for production on a scale never before seen. The San Diego plant had already been approximately tripled in size. A vast new factory was built in 1941 outside Fort Worth, Texas, with a main hall 4,000 ft (1219 m) long and 320 ft (97.5 m) wide. A few miles away at Dallas an almost equal facility was built for North American Aviation, which among other types built the B-24G. By July 1942 Douglas was in volume production at Tulsa, and back in 1941 the largest factory in the United States had been started for Ford Motor Co. at Willow Run, near Detroit, Michigan. Consolidated hired two floors of the Spreckels Theatre in San Diego merely to teach Ford engineers and to assist them to convert over 90,000 B-24 drawings to auto-industry style and terminology. By August 1942 Willow Run was on stream, producing 200 complete B-24s each month, plus a further 150 sets of parts for other assembly lines.
The B-24D saw service in every theatre, and in 1942-43 was by far the most important long-range bomber in the Pacific area. By late 1942 it equipped 15 anti-submarine squadrons (using radar-equipped aircraft) all round the North Atlantic. In July 1942 the US Navy was permitted to share B-24 deliveries, and in August 1943 the Army ASW squadrons were transferred to the US Navy, which eventually operated 977 PB4Y-1 Liberators as well as large numbers of RY-1 and RY-2 transports. These were the equivalent of the US Army C-87A and C-87, which were designed almost overnight as the result of the need for long-haul transports in the evacuation of the Dutch East Indies and went into production at the new Fort Worth plant in April 1942. Named Liberator Express, the C-87 and RY family had 20 easily removed seats and tie-downs for up to 10,000 lb (4536 kg) of cargo loaded through a 6-ft (1.83-m) square door on the left side at the rear; a single gun was kept at the tail for a while but from late 1942 the transports were unarmed. The RAF designation was Liberator C.Mk VII. The C-87A/RY-1 was a VIP model with a luxurious interior normally seating 16. The C-87B was an armed transport, while the C-87C/RY-3/Liberator C.Mk IX was a 1943 model with a tall single fin, lengthened fuselage and oval cowlings with the major axis upright, the air trunks being at top and bottom.
Total production of the B-24D, excluding transports, was 2,738, 2,409 of these coming from San Diego. The most famous exploit of this model was the first of several long-range attacks on the oil refineries at Ploesti, Romania, on 11-12 June 1942 by a dozen aircraft from a special detachment under Colonel H. A. Halverson, which formed the nucleus of the 9th Air Force. Many others went to 8th Air Force bomb groups in England, making their first mission against Lille on 9 October 1942. No fewer than 37 RAF squadrons operated the equivalent Liberator Mks III (British purchase) and IIIA (Lend-Lease), mostly with the Martin top turret but retaining the Boulton Paul tail turret with four 0.303-in (7.7-mm) guns, in Coastal, Bomber and Far East Commands. Coastal Command also used the Mk V with chin and retractable ventral radars, ASV arrays, Leigh light, extra fuel and much special equipment which sometimes included eight forward-firing rockets carried on stub wings on each side of the forward fuselage. The B-24D was developed through block numbers up to 170, bringing in the Dash-65 engine and the Briggs-Sperry retractable ball turret (in place of the tunnel gun), which were to remain standard on subsequent bomber versions. Gross weight climbed to 71,200 lb (32296 kg), much heavier than any other Allied bomber except the B-29 and quite unanticipated when the B-24 was designed. Even the most gentle turns were best made on the autopilot; the controls were both very heavy and very sluggish, and at weights much in excess of 60,000 lb (27216 kg) any rapid manoeuvre (even to avoid a collision) was impossible.
Over the “hump”
The B-24E (RAF Liberator Mk IV) had Curtiss propellers and was the first model built at Willow Run; later some B-24Es were made at Fort Worth and Tulsa. The C-109 was a gasoline tanker conversion of the B-24E (later of the B-24D also) able to carry 2,900 US gal (10978 litres) of fuel in metal tanks in the fuselage, linked to a single socket in the side of the fuselage and with an inert-gas safety system. Later models had Mareng bag tanks, and their main use was to ferry fuel over the ‘Hump’ from Burma into China, especially to support B-29 missions. The XF-7 was a rebuilt B-24D with extra tankage and a large installation of reconnaissance cameras, from which the later F-7 reconnaissance versions were derived, and two one-off experimental prototypes were the XB-24F and XB-41. The XB-24F was fitted with thermal de-icing, and it is surprising it was not adopted because the rubber-boot de-icers were useless if punctured by shell splinters and thousands of man-hours were wasted carefully inspecting them after combat missions. The XB-41 was a ‘destroyer’ (escort fighter) carrying 14 guns in twin dorsal, chin and tail turrets and duplicated waist positions, and extra ammunition.
One of the definite shortcomings of the B-24 in combat proved to be its vulnerability to head-on attack. At best there were only three hand-held guns in the nose, and despite progressive modification to the armour the internal protection was so poor that, both in Europe and over the Pacific Ocean, numerous waist gunners were killed by shells entering at the nose and often killing the pilots en route. Some pilots took to carrying slabs of sheet armour held in front of their bodies by hand during crucial periods. One B-24E (42-7127) was fitted with a nose turret and powered lateral barbettes low on the fuselage sides, flying in this form on 30 June 1943. By the time it flew the decision had been taken to make nose turrets standard, and the vast floods of orders for B-24D and B-24G models were switched to have turrets. North American’s B-24G line had the turret from the start, the selected type being the Emerson A-15; 430 of the B-24G model were built. A new optical bombing station was built in under the turret, and to give the navigator sufficient room and house the 1,200 rounds of nose-turret ammunition the nose was extended by 10 in (25 cm).
Fitting the nose turret to an extended nose was the last major modification, and from mid-1943 the gigantic production machine poured out aircraft superficially almost identical. Those bought under 1941 and early 1942 contracts were designated B-24H, and the 738 built at Forth Worth retained the flat-fronted Emerson electric nose turret as used on the B-24G. The 1,780 built at Willow Run and 582 from Tulsa had the sloping-front Consolidated hydraulic turret, the first Tulsa block being the last B-24s not to have the Dash-65 engine. Called Liberator Mk VI, the RAF and Commonwealth versions usually had the Boulton Paul tail turret, so that all four turrets were of different makes. Made in much larger numbers than any other variant, the B-24J was initially merely a rationalized B-24G or B-24H, with the new C-1 autopilot and M-9 bomb sight and, usually the A-6A (Consolidated) or A-6B (Motor Products) nose turret. From spring 1944 all five plants delivered aircraft to USAAF service depots where any of a wide range of tail armament and equipment schemes could be installed according to the destination theatre. Those for the US Navy, the PB4Y-1, which originally had a B-24D-type nose, switched to the A-6A turret and then, for the main run in 1944, to the nearly spherical Erco nose turret. From April 1944 B-24s were unpainted, and the only significant modifications after that month were the introduction of the improved General Electric (B-22 type) turbocharger, giving higher performance at altitude, and a lightweight Consolidated M-6A twin-gun tail ‘stinger’ (basically manual, with hydraulic assistance, and with a wider field of fire than a turret) which resulted in the designation B-24L. San Diego built 417 of these, and Willow Run 1,250. Some were again rebuilt as B-29 gunner trainers with that aircraft’s complex remote sighting and barbette armament, with designation RB-24L; later they received additional radar as the post-war TB-24L. The many British variants were designated Liberator Mk VI, Coastal Command models being the GR.Mk VI and GR.Mk VIII (the C.Mk VII was a Liberator Express transport series and the C.Mk IX was similar to the US Navy RY-3 with the tall single fin).
New tail – new generations
In March 1943 Consolidated had merged with Vultee to form Convair, and the last major wartime variant was the B-24M with a lightweight Motor Products tail turret, Convair building 916 and Willow Run 1,677. Among the experimental versions were the XB-24P and the Ford-built XB-24Q with a radar-controlled remotely sighted tail stinger, which led to that fitted to the B-47. These were the last of the familiar models with the original tail.
As far back as 1942 it had been clear that a single fin would be better, and on 6 March 1943 a converted B-24D flew with the fin and rudder of a Douglas B-23. After refinement, the whole tail end of this machine was grafted onto another aircraft (42-40234, originally a B-24D but with a nose turret) to become the XB-24K. Ford also fitted 1,350-hp (1007-kW) Dash-75 engines, and the result was a bomber that was considerably faster, had more than double the full-load rate of climb and much better power of manoeuvre. Convair was busy with further major improvements including longer nacelles housing larger oil tanks, an Emerson ball nose turret and lightweight ball turret in the tail, a completely new cockpit window arrangement giving better pilot view, and a further refined tail, and this became the next standard model after the B-24J, the B-24N. Thousands were ordered, the XB-24N flying in November 1944, but only seven YB-24Ns had flown when production stopped on 31 May 1945, 5,168 being cancelled.
Independently, the US Navy had been developing an optimised patrol version with the even taller single fin of the RY-3, low-rated engines without turbochargers and a further lengthened and completely rearranged fuselage. Work began on 3 May 1943, and the first of the prototype PB4Y-2 Privateers flew on 20 September that year.
Type: heavy bomber with crew of 10
Powerplant: four 1,200-hp (895-kW) Pratt & Whitney R-1830-43 Twin Wasp radial piston engines
Performance: maximum speed 303 mph (488 km/h); initial climb 1,100 ft (335 m) per minute; operating radius with 5,000-lb (2268-kg) bomb load 1,080 miles (1730 km)
Weights: empty 33,980 Ib (15413 kg); maximum take-off 60,000 lb (27216 kg)
Dimensions: span 110 ft 0 in (33.52 m); length 66 ft 4 in (20.22 m); height 17 ft 11 in (5.46 m); wing area 1,048 sq ft (97.36 m2)
Armament: one (usually three) 0.5-in (12.7-mm) nose gun, two in dorsal turret, two in tail turret, two in retractable ball turret and two in waist positions; plus a maximum internal bomb load of 8,000 lb (3629 kg)