The Liberator was conceived in January 1939, when General "Hap" Arnold invited Consolidated to come up with a design superior to Boeing’s Flying Fortress. The company’s preliminary data was impressive enough to warrant a contract for a prototype, and the design team under Isaac Laddon went to work in earnest. Their first consideration was range, and they selected the wing design by David Davis for its great efficiency; the wings were shoulder mounted, allowing a capacious fuselage and a twin rudder and fin assembly was chosen. The aircraft had a tricycle undercarriage and the bomb bay was divided into front and rear compartments, with unique roller-type doors which retracted up the sides from the central keel beam.

In the first Liberator, Consolidated Model 32, there was provision for a few hand-held .30-caliber machine guns, and the gleaming prototype, dubbed XB-24 by the Air Corps, flew for the first time on December 29, 1939. By then the Air Corps had already placed an order for seven YB-24s, and thirty-six B-24As for evaluation. The French and British ordered 284 aircraft between them.

Weighing 41,000 pounds gross, the XB-24 was powered by four 1200 horsepower Pratt & Whitney Twin Wasps. The wingspan was 110 feet, and the bomber was 63 feet long. The test flights of the lumbering aircraft were successful, although the maximum speed was slightly less than that of the current model of the Flying Fortress. The range requirements were more than met. During 1940 the YB-24 was delivered, the only difference between it and the XB-24 being the addition of rudder de-icing boots on the tail and wings, increased gross weight, and aircrew spinners which were later discarded.

The fall of France led to their order being transferred to the British, and the first production Liberators were six LB-30As, paid for in cash by England. They were built to British specifications and were used on the Return Ferry Service between Canada and Scotland. The next twenty aircraft, also for England, were known as Liberator Is, and were the first to see operational service. Bristling with aerials and a gun pack containing four 20-mm cannon, they quickly proved themselves in the desperate campaign against the German U-Boats.

The Army Air Forces received their first B-24A in June 1941, one of the nine built. These aircraft went to Ferrying Command, operating between Canada and England. One of the B-24As pioneered the South Atlantic ferry route and in September two of the Liberators flew the Harriman mission to Moscow, and yet another B-24A was the first aircraft over the Greenland ice cap. Two had been detailed to fly reconnaissance over Japanese positions in the Marshall and Carolina Islands, but only one had reached Hawaii by 7 December 1941, and it was destroyed in a hangar at Hickham Field.

The next model was the Liberator II, unique to the Royal Air Force and with an extended nose adding three feet to the aircraft’s length. Four gun Boulton-Paul .303 turrets were fitted in the mid-upper position and in the tail. The first of the Liberator IIs crashed on 2 June 1941, killing Consolidated test pilot William Wheatley, but other Liberator IIs went on to do magnificent work, equipping two squadrons of Bomber Command and three of Coastal Command. Unarmed Liberator IIs flew with the Return Ferry Service, British Overseas Airways, Qantas and Southern Cross Airways, and one was Winston Churchill’s personal transport, the "Commando".

After Pearl Harbor the United States took over fifty-one undelivered Liberator IIs; called LB-30s by the air force, three of these Liberators attacked Kendari on Celebes on 16 January 1942, the first time American-manned Liberators took part in a bombing attack. Others went to Alaska, Hawaii and Panama, while some were used for training and as transports.

The XB-24B was a reworking of the XB-24, with self-sealing tanks, armor and turbo superchargers which resulted in a top speed of 310 miles per hour. This led to nine B-24Cs, which carried a Martin upper turret and Consolidated tail turret, each with two of the .50-caliber machine guns which were quickly replacing the lighter .30 as hard lessons were learned in combat.

The following model of the Liberator was the B-24D, and production went into high gear. Consolidated built 2,415 B-24Ds at their San Diego plant 303 at Fort Worth, and Douglas built ten at Tulsa in Oklahoma. Early B-24Ds had a hand-held nose gun, a Bendix lower turret and four other guns, but later aircraft were equipped with a single ventral gun which fired through the camera hatch, and still later two more nose guns were added, plus waist guns, meaning that the Liberator carried ten defensive guns in all. The bomb load was increased to 12,800 pounds, and maximum gross weight climbed to 71,200 pounds. The hand-held tunnel gun was eventually replaced by the Sperry ball turret.

The first American B-24D unit in combat was the Halpro force – twenty-three Liberators under the command of Colonel Harry Halverson. They were in the Middle East by the middle of 1942, and attacked the Ploesti oilfields, harassed Axis shipping, and helped fill the breach during the crucial phases of the campaign against Rommel. The 98^th Bomb Group joined the Ninth Air Force and went into combat on 1 August 1942, B-24Ds went to war with the Eighth Air Force’s 93^rd Bomb Group on 9 October 1942, and in the Southwest Pacific the 90^th Bomb Group took over the heavy bomber role in Kenney’s Fifth Air Force in November 1942. By the end of the war Liberators would fly with every American air force, and those of several other countries.

The British called their B-24Ds Liberator IIIs when equipped to their specifications, or Liberator IIIAs with American equipment on aircraft supplied under Lend-Lease, and most went to Coastal Command. The U.S. Navy received B-24Ds as YB4Y-1s and these aircraft went to both the Pacific and European Theaters. The first C-87 Liberator Expresses were B-24Ds converted as transports on the production line, and in all 280 C-87s and six C-87As were built, all at Fort Worth. Another B-24D was modified as the XB-41, with fourteen machine guns and provision for 11,000 rounds of ammunition; this was to be a "bomber escort" but was never tested operationally.

The B-24E differed little from its predecessor, and one was modified in late 1943 as the XC-109, a fuel tanker with nose and bomb bay fuel tanks.

Combat in Europe and the Pacific had revealed that the B-24D was vulnerable to head-on attack, and various solutions were tried. Twin nose guns, lashed together, were used in Europe, but they were difficult to use, although some crews maintain it was a better arrangement than the later nose turret, as far as overall performance of the aircraft was concerned. The 90^th Bomb Group in the Southwest Pacific pioneered the installation of a consolidated tail turret in the Liberator’s nose, and similarly successful work was carried out at the Hawaiian Air Depot. Later Navy B-24Ds were equipped with the distinctive Erco turret, which extended the nose about three feet. Some B-24Ds were fitted with twin waist guns, the most successful experiment being in the 44^th Group, where Lieutenant Bill Strong and his crew designed a special mounting for use in their plane, "Baldy and His Brood".

Ford Motor Company began their Liberator production with 480 B-24Es, built at the huge Willow Run plant in Michigan, and another 311 B-24Es were built by Douglas and Consolidated at Fort Worth. The sole XB-24F was a modification of the B-24D, with a thermal de-icing system.

There were 430 B-24Gs, all built in Dallas by the fourth producer of the Liberator, North American Aviation. These aircraft were not all the same – the first twenty-five were without the electrically powered Emerson nose turret, and although later aircraft were equivalent to the B-24H, they were not redesignated.

The first Liberator to be fitted with a nose turret on the production line was the B-24H, and Consolidated built 738 at Fort Worth, with Emerson electric turrets. Another 1,780 were built at Willow Run, and 582 at Tulsa, Ford and Douglas using the Motor Products hydraulic turret.

The most prolific model of the Liberator was the B-24J, built at all five factories and differing little in essentials from the B-24H. Around 1,200 went to the Royal Air Force, others became F-7As and F-7Bs, equipped with sic aerial cameras, and more went to the Navy, where they were still called PB4Y-1s, carrying the Erco nose turret. Ford built 1,587 B-24Js, North American 536, Douglas 205, Consolidated Fort Worth 1,558 and San Diego 2,792. There were 6,678 B-24Js in all.

Similar to the B-24J, the B-24L was fitted with a lighter tail turret designed by Consolidated’s Tucson modification center. This gave a greater field of fire, was easier to manipulate and saved some two hundred pounds in weight. Ford produced 1,250 aircraft at Willow Run, and the other 417 were built by Consolidated at San Diego.

The last model of the Liberator to see quantity production was the B-24M, which was fitted with a light power tail turret, and 2,593 aircraft were built at San Diego and Willow Run. The XB-24P was a modified B-24D which was used for fire control research, and the XB-24Q was a B-24L with an experimental radar-controlled tail installation.

Back in 1942 it had been reasoned that the B-24 would have greater stability with a single fin, and a B-24D was modified and designated XB-24K in 1943. The high tail test aircraft proved the theory regarding stability and control and in April 1944 the decision was made that the twin tail assembly would no longer be used. However, only the XB-24N and seven YB-24Ns were built before 31 May 1945, when Liberator production was ended, and other orders for the single-tailed B-24N were cancelled. The Navy received 739 single-tailed Liberators which they had contracted for – these were heavily modified and known as PB4Y-2 Privateers.

In all 18,482 Liberators were built, but obsolescence claimed the bomber quickly, until by 1951 only one B-24 remained on the USAF’s inventory.