In order to meet the projected demand for the B-24, in early 1941 the government established the Liberator Production Pool Program. Under this program, Consolidated would set up a new plant in Fort Worth, Texas to supplement the Liberator production in its main San Diego plant and Douglas would open up a similar plant for Liberator production in Tulsa, Oklahoma. The initial plan was for the Douglas/Tulsa plant to put together complete Liberators from sub-assemblies and components provided to it by Consolidated until it acquired enough experience to build complete aircraft on its own.
Shortly thereafter, the Ford Motor Company joined the Liberator Production Pool Program as a third member. Ford planned to build Liberators at an entirely new plant at Willow Run near Detroit. Initially, Ford was assigned the task of providing components for final assembly by Consolidated/Fort Worth and Douglas/Tulsa, but in October of 1941 Ford received permission to assemble complete Liberators on its own.
In January of 1942, following Pearl Harbor, North American Aviation was given a contract for the manufacture of B-24s at its Dallas, Texas plant. This brought the total number of plants involved in Liberator production to five.
By early 1942, the Army had formalized its initial Liberator production plan. Primary manufacturers of the B-24 were to be Consolidated/San Diego, Ford/Willow Run, and North American/Dallas. These aircraft were to be designated B-24D, B-24E, and B-24G respectively. Consolidated/Fort Worth and Douglas/Tulsa were to carry out the final construction of planes by putting together sub-assemblies provided by the other three plants. Eventually, Consolidated/Fort Worth would also become a primary manufacturing center. In addition, the Ford plant at Willow Run was designated as the prime contractor for B-24 spare parts.
The Willow Run plant was truly gigantic. It was built on a 65-acre site and was almost a quarter of a mile wide and a half-mile long. It had a 90-degree bend in the middle of its length. This bend had supposedly been put there at the insistence of Henry Ford himself. According to local legend, the length of the plant had been miscalculated by the architects during the initial design work, and the bend had to be introduced in order to prevent the plant from extending into the next county where the taxes were higher. This bend came to be known as the "tax turn", and Liberators had to take a rather awkward 90-degree turn as they progressed down the assembly line.
The first B-24Ds for the USAAF were manufactured by Consolidated/San Diego in January of 1942. As part of its participation in the Liberator Production Pool, the Consolidated/San Diego plant began to supply sub-assemblies for B-24Ds to Consolidated/Fort Worth in May of 1942, and to Douglas/Tulsa in August 1942 for final assembly.
The first Ford-built Liberator rolled off the Willow Run line in September of 1942. The Ford-built Liberator was designated B-24E. The Ford plant had lots of initial startup problems, due primarily to the fact that Ford employees were used to automobile mass production and found it difficult to adapt these techniques to aircraft production. Ford's plant at Willow Run was beset with labor difficulties, high absentee rates, and rapid employee turnover. The factory was nearly an hour's drive from Detroit, and the imposition of wartime gasoline and tire rationing had made the daily commute difficult. In only one month, Ford had hired 2900 workers but had lost 3100. Henry Ford was cantankerous and rigid in his ways. He was violently anti-union and there were serious labor difficulties, including a massive strike. In addition, Henry Ford refused on principle to hire women. However, he finally relented and did employ "Rosie the Riveters" on his assembly lines, probably more because so many of his potential male workers had been drafted into the military than due to any sudden development of a social conscience on his part. At the request of the government, Ford began to decentralize operations and many parts were assembled at other Ford plants as well as by the company's sub-contractors, with the Willow Run plant concentrating on final assembly. The bugs were eventually worked out of the manufacturing processes, and by 1944, Ford was rolling a Liberator off the Willow Run production line every 63 minutes. A total of 6972 Liberators were built at Ford, and 1893 knock-down parts were provided for other manufacturers.
The last member of the pool to produce Liberators was North American/Dallas. The version of the Liberator built by North American was designated B-24G. The first B-24G Liberators rolled off the line at Dallas in late 1942.
Since five different manufacturing plants were now building the Liberator, it was necessary for the USAAF to keep track of which plane was built by which plant for maintenance and spare parts purposes. This was done by adding a manufacturer identification code to the designation scheme after the block number to identify the builder of a particular airplane. These letters identified the particular plant which was responsible for the construction of the aircraft. The letters designating the five members of the pool were as follows
CO Consolidated/San Diego CF Consolidated/Fort Worth DT Douglas/Tulsa FO Ford/Willow Run NT North American/Dallas
However, since each plant in the pool would often use sub-assemblies and components provided by the other members, even this system was not completely adequate to tell maintenance people which factory was really responsible for any given plane. The general rule seems to be that the manufacturer code assigned to a particular aircraft corresponded to the factory that was responsible for its final assembly, with the series letter (D, E or G) identifying the primary manufacturer.
The version of the Liberator that underwent primary manufacture at Consolidated/San Diego was designated B-24D. When the B-24D was completely assembled at San Diego, it was designated B-24D-CO. However, Consolidated/San Diego also shipped parts and components of B-24Ds to Consolidated/Fort Worth and to Douglas/Tulsa for final assembly. B-24Ds assembled by these plants were designated B-24D-CF and B-24D-DT respectively.
The B-24E was the version of the B-24D that underwent primary manufacture by Ford at Willow Run. There were significant differences between the B-24E and the other two versions. Not only did Ford build complete planes, but it also supplied components of B-24Es for final assembly at Douglas/Tulsa and at Consolidated/Fort Worth. B-24Es built and fully assembled at Ford were designated B-24E-FO, but those assembled by Douglas/Tulsa and Consolidated/Fort Worth out of parts supplied by Ford were designated B-24E-DT and B-24E-CF respectively.
The version of the Liberator built by North American/Dallas was designated B-24G. It differed little from the Consolidated/San Diego-built version. Since North American/Dallas was only a primary manufacturer and did not supply components to the other members of the pool, all B-24Gs bore the NT manufacturer's letters.
As might have been expected, the production pool system did cause lots of problems with standardization of components and equipment. Variants coming from the various members of the pool would often have significant detail differences from each other, leading to a spare parts and interchangeability nightmare. There were often significant differences between the various production blocks of the same model Liberator and sometimes differences even WITHIN a production block. Parts for Liberators built at different factories were often not interchangeable with each other, and all four factories involved in primary manufacturing produced Liberators of similar variants but of vastly different detail specification. Even the two Consolidated plants suffered from this problem.
With the introduction of the B-24J, all five members of the pool (both primary manufacturers and sub-assemblers) converted to the production of this version.
Since Liberator production rates were extremely high, it became difficult to introduce changes dictated by field experience onto the production line in a timely fashion. Consequently, newly-constructed Liberators were often already obsolescent as soon as they rolled off the line. For this reasons, a series of modification centers were established for the incorporation of these changes into new Liberators following their manufacture. There were seven known modification centers: Consolidated/Fort Worth, Oklahoma City Air Materiel Center, Tucson Modification Center, Birmingham Depot, Northwest Airlines Depot, Martin-Omaha, and Hawaiian Air Depot.