![B-24 Liberator bomber aircraft World War II](https://static-ssl.businessinsider.com/image/5a468d564aa6b53c358b6ef8-1600/ap44010101130.jpg)
(AP Photo)
B-24 Air Force on a mission in 1944.
As the US military was looking to expand production of Boeing's B-17 bomber in the late 1930s, Washington asked Consolidated Aircraft to start producing the plane.
But after a visit to Boeing's factory in Seattle, Consolidated proposed a totally new aircraft.
Consolidated was granted a design study for a new bomber with specifications exceeding those of B-17. The company quickly turned out a new bomber design, and it received a contract for a flyable prototype, the XB-24, in March 1939.
On December 29, 1939, the XB-24 took its first flight - just a few months after Nazi Germany's Blitzkrieg swept over Poland in September. By spring 1940, Adolf Hitler's forces were marching through Western Europe and Consolidated's new bomber was sent to the British.
![B-24 Liberator bomber aircraft World War II](https://static-ssl.businessinsider.com/image/5a468eb8b0bcd51d198b7678-1194/ap4310060118.jpg)
(AP Photo)
President Franklin D. Roosevelt at the commissioning of four B-24 Liberator four-engined bombers and their delivery to American-trained Yugoslavian combat crews, in Washington, DC, October 6, 1943.
1940 came to a close with Nazi Germany ascendant.
US had not yet entered the war, but President Franklin Roosevelt exhorted American industry to shift from peacetime production and start churning out the materials needed to bolster Allied forces teetering on the brink of defeat.
"Guns, planes, ships, and many other things have to be built in the factories and the arsenals of America. They have to be produced by workers and managers and engineers with the aid of machines which in turn have to be built by hundreds of thousands of workers throughout the land," Roosevelt said on December 29, 1940. "We must be the arsenal of democracy."
The B-24 bomber, dubbed the Liberator, would become a mainstay of that arsenal. The hearty bomber saw service in all theaters of the war but played an essential role in the effort to pummel German forces in Europe.
"The B-24 has guts," the Army Air Force's pilot-instruction manual said. "It can take it and dish it out. It can carry a bigger bomb load farther and faster, day in and day out, than any airplane that has passed the flaming test of combat."
Below, you can see how the vaunted B-24 went from prototype to the most mass-produced aircraft in history - helping carry Allied forces to victory along the way: