Over 19,000 B-24 Liberator bombers were manufactured by the US during the Second World War, making it the most widely-produced American aircraft of the period.
In 1938, in response to the deteriorating political conditions in Europe and the Pacific, the US decided to ramp up production of its B-17 bomber. As part of this effort, the Army Air Force contacted the Consolidated Aircraft Corporation to ask them to produce Flying Fortresses under a license from Boeing. But Consolidated did not want to manufacture a design which was then already four years old (and it especially did not want to license a design that had been made by another company). So instead, Consolidated offered to design and make a new heavy bomber to the Army’s specifications.
The project was given the working name Model 31. It would be a long-range four-engine heavy bomber with a longer range, faster speed, and heavier bomb load than the B-17. Much of the design, including the high-aspect-ratio wings and the distinctive forked tail, was based on the company’s earlier Model 31 flying-boat seaplane. The fuselage was drawn up with two bomb bays. The first prototype flew in December 1939.
The US immediately ordered a number of the new B-24A bombers for the Army and additional YB-24 patrol bombers for the Navy. But with the war in Europe already raging, the first production runs were for the LB-30 export model. Orders came in from France for 120 bombers and Britain for 160. Many of these were used for coastal and anti-submarine patrols, and one of them was modified to serve as Winston Churchill’s personal transport aircraft. When France surrendered to Germany in May 1940, its LB-30s had not yet been delivered, and they were subsequently diverted to England. The US Army Air Corps received its first operational B-24D models in May 1942.
Improvements quickly followed. The original production B-24A used Pratt & Whitney R-1830-33 Twin Wasp engines, which were then upgraded with a supercharger. These were themselves soon replaced by the new turbo-supercharged 14-cylinder R-1830-41, which gave a top speed of 310 mph. Throughout the war the Liberator was constantly modified, with each new model introducing a change in armament or configuration. Gun blisters were added to the sides of the fuselage, and ball turrets to the belly and chin. The number of guns grew from six to eleven, and the bomb load expanded from 8,800 pounds to 10,800 (using external bomb racks). The unique bomb bay doors rolled up into the fuselage, preventing the drag that resulted from open “barn doors”. Some ground-attack versions were fitted with four 20mm cannon in the nose.
As the war progressed, older models were sent back to the factory to be refitted and upgraded. At some points in time the factories were unable to keep up with all the changes and bombers were already obsolete as they were produced, and ended up being sent directly from the assembly line to be upgraded.
Unarmed versions were used as C-87 cargo aircraft and as C-109 fuel tankers, and cameras were fitted for reconnaissance flights. Naval patrol versions, designated PB4Y and used for anti-submarine work, were equipped to carry depth charges and, towards the end of the war, were modified to carry an experimental radar-guided anti-ship missile known as the “Bat”.
To keep up with the heavy demand, Consolidated produced B-24s at both of its aircraft plants, and also licensed their production to other plants run by Douglas Aircraft, North American Aircraft, and the Ford Motor Company. By the spring of 1944, the Ford plant alone was churning out a finished B-24 every 100 minutes, running 24 hours every day. In all, a total of 19,200 Liberators of various models were produced.
The B-24 saw service in virtually every theater. In Europe, although it was faster than the B-17 it could not reach as high an altitude, and it often flew in below the Flying Fortresses. One notable raid carried out by the B-24s was on the Ploesti oilfields in Rumania. In the Pacific, the B-24’s high speed and long range were an advantage, and as the B-17s were diverted to Europe, the B-24 became the principle heavy bomber used by the Allies. In all, B-24 bombers dropped a total of 630,000 tons of bombs in all theaters.
But many aircrews did not like the Liberator. It was not as rugged as the B-17 and could not withstand as much battle damage. It was also not an easy plane to fly, and many were lost in crashes and training accidents. The gas tanks had a tendency to leak, sometimes producing mid-air explosions.
After the war, a number of B-24s remained in service with the Coast Guard as patrol aircraft. The Indian Air Force also inherited a number of B-24s from the British, which continued to fly for a number of years (a number of them flew in the Berlin Airlift in 1948).
Today, around a dozen WW2 B-24 Liberators still survive, in museums in the US, UK, Canada, Australia, and India. Many of these are from the group of 36 that was abandoned in India at the end of the war and restored by the IAF. One of these is on display at the Pima Air and Space Museum in Arizona, where it was obtained from the Poona Air Force Base. This B-24J was manufactured in Ft Worth TX and sent to the RAF’s Southeast Asia Command. The US Air Force Museum in Dayton OH has a B-24D that was built in San Diego and flew 56 missions in Italy from 1943 to 1944. After the war it was returned to the US and placed in storage. The Museum acquired it in 1959. There are two airworthy examples surviving, in Massachusetts and Texas, which often travel to air shows.
Hidden History 
The (thankfully renamed) Commemorative Air Force flies a survivor that’s been to Greenville a few times. I was driving through town on a clear day 10 or 15 years ago, looked up through the windshield at a movement that caught my eye, and there was a desert-tan B-24 overhead.
That’s a strange sensation for an aviation buff. :>)