The Thompson is an American sub-machine gun, invented by John T. Thompson (1860- 1940) in 1919, that became infamous during the Prohibition era. It was a common sight in the media of the time, being used by both law enforcement officers and criminals. The Thompson was also known informally as: the â€œTommy Gunâ€, â€œTrench Broomâ€, â€œTrench Sweeperâ€, and â€œChicago Typewriterâ€. The Thompson was favored by soldiers, criminals, police and civilians alike for its ergonomics, compactness, large .45 ACP cartridge, reliability, and high volume of automatic fire. It has since gained popularity among civilian collectors for its historical significance. It was during Thompsonâ€™s career in the military, around the time of the Spanish-American War (1898) that he met 2nd Lt. John H. Parker, who had learned that Thompsonâ€™s unit, based in Tampa, Florida, had fifteen Gatling guns with no orders as to how they were to be disposed. Parker not only wanted to use them in the war, but also planned to create a new Gatling gun detachment and prove the effectiveness of rapid-fire weapons (an ambitious undertaking, given that the US Army had been reluctant to even upgrade its antique single-shot Springfield rifle). Thompson was very receptive to Parkerâ€™s idea and not only gave him the guns but a large supply of ammunition. Parker went onto make a name for himself at the Battle of San Juan Hill but Thompson decided to try and correct the sorry state of American small arms. He was the first Army Ordnance Department officer to recognise the need for fully automatic pistols and rifles. As the years went by, Thompson grew tired of fighting the Army about the need to adopt automatic weapons, so he surprised everyone and retired in 1914, on the eve of the Great War. He took a job at the Remington Arms Corporation managing the construction of the worldâ€™s largest rifle factory at Eddystone, Pennsylvania, built to support the war in Europe. At its height, it produced 2,000 rifles a day. These included the .303in Pattern 1914 Enfield for the British Army and the 7.62mm Mosin Nagant rifle for the Russian Army. With success in managing the Eddystone Factory, Thompson decided to continue his quest for a fully automatic weapon, attempting to design and build a weapon in his spare time, using his own capital and then submit it to the Army as a civilian inventor. Thompson hoped that his weapon would not only shorten the war in Europe but also earn him a lot of money. There were three main designs at the time, none of which quite met his requirements. The recoil system was mainly used in medium and heavy machineguns, however there were many moving parts and reliability could be a problem. The gas system had the same drawbacks as the recoil system but whereas in the recoil system, it is the barrelâ€™s rearward movement that cycles the weapon, in the gas system a hole is tapped in the barrel which bleeds gas off after a round is fired, to drive a piston that cycles the system. The third design is the blowback system, mainly used in semi-automatic handguns and relies on the propellant gas pressure to literally â€˜blowâ€™ the bolt rearward. This action powers the sequence of ejecting the spent cartridge and chambering a new one. This type of weapon is pretty simple as they do not have a locking breech, but depend on the forward inertia of a heavy bolt, driven by a recoil spring, to keep the breech closed at the point of maximum pressure. Such a system would seem to be ideal for a lightweight, fully automatic weapon due to the lack of moving parts, reliability and its simplicity, but in practice itâ€™s only usable with low-powered pistol ammunition, as high-powered rifle ammunition creates very high chamber pressures, overcoming the inertia in the bolt and blowing it back prematurely. To build a personal sub-machinegun, Thompson had to find a way of making a simple but effective breech lock. For over a year, this technical problem was insurmountable, until he came across Patent No. 1,131,319 at the US Patent Office â€“ â€œA Breech Closure for Firearmsâ€, granted to a retired US Navy Commander, John B. Blish. The â€˜Blish Lockâ€™ was a breech locking mechanism that could be used with a blowback system. It delayed the blowback of the bolt until the chamber pressure had dropped to an acceptable level. Thompson could now produce his gun â€“ he had realised that few would accept a pure blowback system and it would help sales to say that the Blish Lock held the chamber closed until pressure dropped to a safe level. The design came from the observations Blish had on large naval guns, where guns firing relatively light charges tended to have their breech blocks unscrew and fly open, while those that had relatively large charges tended to remain shut. Blish concluded that certain metals had a tendency to adhere to each other when subjected to very high pressure, with a force that was greater than just normal friction. This principle of metal adherence has since become known as the Blish Principle. In late 1915, Thompson contacted Blish, who was excited to learn about Thompsonâ€™s work and was positive that the lock would be suitable. Thompson worked out an arrangement where he would use the lock in exchange for a percentage of stock in the company Thompson was planning to start. Thompson found financial backing for his company from the Tobacco tycoon, Thomas F. Ryan and in 1916, Auto Ordnance Corporation was founded. Ryan was given a controlling interest in the company with around 18,000 out of 40,000 shares, while Blish was given 1,500 for the use of his patent and another 10,000 divided up amongst Thompsonâ€™s family.