More B-24 Liberators were built than any other American warplane, and more than any bomber type in any other country in the world. Although less famous than the B-17, the B-24 was much more widely used.
The Liberator began in January 1939, when the Chief of the Army Air Corps decided that a second heavy bomber type should join the B-17 in production. Consolidated Aircraft’s chief designer, Isaac M. Laddon, could respond with Model 32, which used a new Davis airfoil on a high aspect ratio wing with Fowler flaps to add lift for takeoff and landings.
Since this wing was already being built on the Model 31 flying boat, and Consolidated had also flown the four-engine XPB2Y-1 bomber for the Navy, Laddon was able to present a proposal to Wright Field on January 30, and begin wind tunnel tests on a model by February 16. The XB-24 prototype was ordered March 30, 1939, and additional orders were placed for seven YB-24s on April 27, and 38 B-24As on September 20.
What became the most important flight from San Diego’s Lindbergh Field was made on Friday, December 29, 1939, by William Wheatley, only nine months after the original contract was approved. The XB-24 had the first tricycle landing gear flown on a large bomber. The nose wheel permitted faster landings and take-offs, and thus allowed a heavier wing loading on the narrow wing. Power plants were four Pratt & Whitney R-1830-33 Wasps of 1,000 hp at 14,500 feet.
A bombardier’s Plexiglas enclosure began the nose of the deep fuselage, which terminated behind twin rudders with a tail gunner’s position. Armament included three .50-caliber hand-operated guns fired after opening panels in the rear fuselage top, bottom, and tail, while four .30-caliber guns were provided for two sockets in the nose and two mounts at the waist panels. Eight 1,130-pound bombs could be accommodated, twice the capacity of the B-17’s bay, and the wing tanks could hold 40 percent more fuel.
Problems discovered on early tests led to exchanges of the twin fins with the Model 31, and were solved by extending the horizontal tail from 22 to 26 feet, beginning with the 23rd test on April 12, 1940. Slots in the outer wings were found an unnecessary drag. The prototype’s speed was measured at from 291 to 298 mph during the first 30 flights, instead of the 311-mph promised by the specification.
On July 26, 1940, the Air Corps ordered that leak proof fuel tanks and B-2 turbosuperchargers be installed. Redesignated XB-24B with 1,200-hp R-1830-41 Wasps and with wing slots deleted, the reworked prototype would be flown February 1, 1941. Each turbosupercharger added 135 pounds of weight, but they raised critical altitude to 25,000 feet, where top speed could be over the 320-mph level.
Until these improvements could be incorporated into production B-24s for the Air Corps, Consolidated could export earlier models. In April 1940, the French became interested in the LB-30 version with commercial R-1830-S3C4G engines. By the time a contract was made in June 4, 1940, France was near defeat. Britain took over the contract on June 17, specifying 165 LB-30s with self-sealing fuel tanks, armor, and power-operated turrets. c="http://pagead2.googlesyndication.com/pagead/show_ads.js">
These features, plus turbosuperchargers, were also specified for the future Air Corps B-24C/D versions, by a contract change dated June 24, 1940. Delivery on the B-24s ordered in 1939 was deferred by the Air Corps announcement on November 9, 1940, that 26 would go to Britain, and be replaced later by modernized B-24C/D models. The RAF aircraft would be delivered with commercial R-1830-S3C4G engines and without armament.
The first YB-24 was painted in RAF colors when first flown on November 19, 1940, and was similar to the original XB-24 except for R-1830-S3C4G engines, omitting wingtip slots, and adding deicers. Six were accepted in December and redesignated LB-30A. They provided Britain with fast transatlantic mail and ferry service, and in 1943 flew a risky route to Moscow.
Using R-1830-33 Wasps, the seventh YB-24 added self-sealing fuel tanks and 637 pounds of armor. First flown on March 4, 1941, it was delivered in Army olive-drab paint to Wright Field on April 7, seven months behind schedule, and assigned to the Ferry Command school on July 5. As the prototype for the B-24A, it was armed with six .50-caliber hand-operated guns in the rear fuselage’s top, waist, bottom, and tail openings, with two .30-caliber guns for the nose enclosure’s upper and lower sockets.
Design gross weight of all early B-24s was “assumed” to be 41,000 pounds, although this would allow only six crewmen, 854 gallons, and 2,500 pounds of bombs. There was room to add 6,000 pounds of bombs or another 1,000 gallons, as the mission demanded. Actual combat would require at least a third more gross weight.
The first 20 B-24As were delivered with R-1830-S3C4G Wasps from March 29 to May 26, 1941, as the RAF’s Liberator I (LB-30B), serials AM910/929. A hard landing in Britain wrecked one, and three became transports.
The other 15 joined No. 120 Coastal Command Squadron, based at Nutts Corner in Northern Ireland, the first RAF unit able to cover the mid-Atlantic submarine gap. After gradually learning to find their difficult targets, they began, in October 1942, attacks that sank eight U-boats, five by Liberator AM929’s crew alone.
Equipment installed at Prestwick, Scotland, included a complicated radar installation, the ASV Mark II, with both forward and sideways-looking aerial arrays. Six to eight 250-pound depth charges could be carried on 16-hour patrols, along with four 20-mm fixed guns in a tray under the fuselage and six .303-caliber guns (British Brownings), paired on the waist and tail mounts. Another LB-30B, AM927, remained in the U.S. after an accident, became a Consolidated company transport and prototype for the C-87, and lasted many years after the war with the Confederate Air Force as the oldest Liberator still flying.
Nine B-24As accepted by the Army from June 16 to July 10, 1941, had R-1830-33 Wasps like the YB-24. Mounts for six .50 and two .30-caliber guns and 519 pounds of armor were provided, but these planes went to the newly organized Army Air Force Ferry Command, which retained only a tail gun and used them to pioneer intercontinental routes vital to Allied cooperation. They were the only Army planes with enough range for flights like the mission carrying Americans from Scotland to Moscow in September 1941. Passengers sat for 15 hours on bare benches in the unheated bomb bay.