By 1940, Nazi forces had overrun nearly all of Europe. Britain itself faced invasion across the Channel and was short of troops and weapons. In desperation, the British military designed a crude sub-machine gun, known as the Sten, that could be manufactured quickly and cheaply from stamped parts and steel tubes. The gun was manufactured by the thousands and was widely distributed to be used in the defense of the island.

As it turned out, the Nazis lost the air Battle of Britain and their planned invasion never happened.

In 1942, a Polish military officer had an idea, inspired by the Sten--why not produce a cheaply stamped pistol that could be easily produced in large numbers and dropped behind the enemy lines to arm the various Resistance networks that had been formed in the occupied territories?

The idea appealed to some officers in the American Joint Psychological Committee, in charge of psychological warfare. They concluded that not only would a mass drop of thousands of weapons be of practical use in arming the Resistance fighters, but it would also hurt German morale by making the occupation troops fearful. They assigned the task to a team lead by George Hyde from the Inland Manufacturing Division of General Motors, and within a few weeks he had produced a design for a crude single-shot pistol dubbed the FP-45 Liberator.

Disguising the project as a flare projector (FP) to hide it from Nazi spies, the gun was deliberately designed to be as cheap and easily made as possible. There were only 23 parts: the barrel was a simple four-inch unrifled steel tube, and the rest of the gun was made from stamped pieces of sheet metal. It used the same .45 caliber ammunition as the Colt .45 automatic pistol. Each Liberator cost about $2.10 to make (about $35 in today's dollars). Some wags dubbed it the "Two-Buck Gun", or the "Woolworth Gun", after the five-and-dime store.

To load the weapon, the user had to twist the breech-block at the back of the pistol open and insert a single .45-caliber cartridge into the firing chamber, then close the block. Squeezing the sheet-metal trigger fired the pistol. After firing, the pistol could be reloaded by opening the block, pulling out the spent cartridge case (it often wouldn't come out, so the pistol came with a wooden dowel that was poked down the barrel to push the cartridge case out the back), inserting a fresh cartridge, and closing the block again. Testing done with the prototypes showed that the welded seams would often start splitting after just 10 rounds had been fired through the gun--and none of the tested pistols were still usable after 50 rounds. In humid conditions such as the Pacific islands, the unfinished metal in the guns often rusted and corroded within a few weeks.

But the Liberator was not intended as a combat weapon: rather, it was intended to be single-use and disposable. The idea was that a Resistance fighter could hide the Liberator in his pocket, walk up to an unsuspecting German trooper, pull the pistol and shoot him at close range, and then take his weapons and ammunition. The unrifled barrel gave the Liberator an effective range of fewer than ten feet, and the big .45 caliber cartridge was chosen because it was likely to kill or disable its target with just one shot.

Because the Inland Division was already busy producing M-1 rifles for the Army, the manufacture of the Liberator pistol was assigned to the Guide Lamp Division in Anderson, Illinois, a division of General Motors which in peacetime had been making automobile headlights and turn signals. About 300 GM workers were assigned to the task, and over a period of 11 weeks, they produced over a million Liberators. The finished pistols were packed in waxed-cardboard boxes with ten rounds of .45 caliber ammunition (which could be stored inside a hollow compartment in the pistol grip), a wooden dowel (for reloading), and a cartoon-illustrated instruction sheet showing how to load and use it (because the cartoon did not use verbal instructions, it could be dropped anywhere for any language group). The entire process, from design to manufacture, had taken about six months. Each gun had taken an average of 6.6 seconds to make.

Once manufactured, the Army, under both General Eisenhower and General MacArthur, declared that they saw no use for them, and the Liberators were turned over to the Office of Strategic Services (OSS), the American forerunner of the CIA which was in charge of Resistance activities in the occupied territories. Unlike the Army Psychological Warfare guys, however, the OSS never saw any real practicality in the weapon either, and never made any large-scale effort to distribute it to Resistance fighters, though about 100,000 Liberators were sent to guerrilla forces fighting the Japanese in the Philippines and China. Only about 25,000 pistols were dropped to Resistance groups in Europe. There are no documented instances of any Japanese or Nazi occupation trooper actually being killed by a Resistance fighter or guerrilla armed with a Liberator pistol. Most Resistance forces were supplied with the more-effective Sten instead.

At the end of the war, most of the Liberators sat unused in their boxes. To save storage space, they were ordered destroyed. As a result, today authentic Liberators are very rare and are highly prized by military collectors. A WW2 Liberator in good condition (and with the rare original box and equipment) can sell for over $2000.

Although the Liberator was not exactly a military success, during the Vietnam War in the 1960's the CIA resurrected the idea, and produced another single-shot disposable pistol called the "Deer Gun", intended to be dropped in behind enemy areas. The Deer Gun was made from cast aluminum with a short steel barrel and fired the 9mm Parabellum cartridge. It was loaded by unscrewing the barrel, inserting the cartridge, then screwing the barrel back on. About 1,000 Deer Guns were made in 1964, at a cost of about $3.95 each. After some field testing, it was never mass-produced, and the originals were destroyed.