Development of the Thompson Sub Machinegun

When John Thompson set out to build his gun, he knew that the heart of a machinegun lies in the design of it’s breech locking and feeding mechanisms. Thompson was aware of the designs used in other guns of the day, but none was appropriate for his needs.

Recoil actuated systems were popular in the heavy and medium machineguns of the era, but these used many moving parts that were heavy and prone to failure. The Recoil system uses the rearward thrust of a movable barrel to unlock the breech, eject the spent cartridge case, insert a fresh cartridge, re-lock the breech and fire the next round.

The Gas actuated system had the same drawbacks as the Recoil system. The Gas system employs a small vent hole drilled into the barrel that bleeds off some of the high pressure gasses that propel the bullet down the barrel. The vented gas pressure is routed back to the breech area where it drives a piston that performs the same unlocking, ejection, loading re-locking and firing sequence as the Recoil operated guns.

The third system, used mostly in semiautomatic handguns, employed a technique referred to as ‘Blowback’. These guns relied on the propellant gas pressure to literally ‘blow’ the bolt rearward. This action powered the sequence of ejecting and loading the next round. Guns using the Blowback process are simple because they do not have a locking breech. They depend on the forward inertia of a heavy bolt, driven by a recoil spring, to keep the breech closed at the point of peak chamber pressure. The Blowback system would seem to be the ideal choice for use in a lightweight machinegun because of it’s simplicity, lack of heavy moving parts and reliability, but in practice it’s only usable with low powered pistol ammunition. High power rifle ammunition creates much higher chamber pressure. Pressure at this level that would overcome any inertia in the bolt, blowing it back prematurely. This would cause cartridge cases to be ejected during peak pressure; exposing the operator to the hazards of ruptured brass and explosive gasses.

To build his personal machinegun Thompson had to find a way to make a simple but practical breech lock. This one technical problem had him stumped. Finally, after more than a year of research he found the answer to his problem. While searching the United States Patent Office files, he came across patent No. 1,131,319. A “Breech Closure for Firearms”. The patent was granted to a retired Navy Commander named John Bell Blish. The ‘Blish Lock’ was essentially a breech locking mechanism that could be used on a Blowback operated firearm. The lock delayed the Blowback of the bolt until the chamber pressure had diminished to an acceptable level. What this meant to Thompson was that it was now possible for him to build his gun.

The Blish Lock was the result of observations made by Blish, of large Naval guns. He noticed that guns firing relatively light charges tended to have their breech blocks unscrew and fly open. But the breech blocks of guns firing heavy charges remained closed. Using his mathematical and analytical training, he concluded that metals have a tendency to adhere to each other with a force much greater than friction, when subjected to very high pressure. This principle of metallic adhesion has since come to be known as the Blish Principle. It didn't take Blish very long to put this knowledge to use in a delayed Blowback breech lock. He developed a working model that used a simple wedge as the lock, and was eventually awarded a patent.

Some time in 1915 Thompson contacted Blish. Blish was very excited about Thompson’s idea, and was sure his lock was suitable for the purpose. So Thompson worked out an arrangement where he could use Blish’s breech lock, in exchange for a block of stock in the Arms company that Thompson planned to start. Now, all that remained for Thompson to do was to secure the financial support needed for such a large undertaking.

Thompson found financial backing for his machinegun project from Tobacco tycoon Thomas Fortune Ryan. In 1916 Auto Ordnance Corporation was founded, with Ryan providing all of the development and operating funds. In exchange he was given a controlling interest in the company. Of the 40,000 shares of stock authorized, Ryan was given about 18,000. 1,500 shares were given to John Blish for the use of his patent, and about 10,000 were divided up among Thompson’s family; including his daughter-in-law who was the daughter of Ryan’s friend and business associate, George Harvey. Although this arrangement gave Auto Ordnance Corp. it’s start, it would later lead to the eventual near ruin of the company.

Auto Ordnance Corp. began operations in the spring of 1916 with two employees. Theodore H Eickhoff and George E. Goll. Eickhoff was Thompson’s assistant at the Army Ordnance Dept., and was given the title of Chief Engineer. Goll was an unemployed railroad fireman when Thompson hired him as his chauffeur. Recognizing his intelligence and mechanical aptitude, Thompson offered him the job as Eickhoff’s assistant. Under Thompson’s direction, it was these two men who would become the principle designers of the Tommy Gun. Later on Oscar Payne would join Auto Ordnance Corp. and be responsible for many of the design innovations that made the gun a success; including the self-oiling system and high capacity rotary drum magazine.

At the start, Auto Ordnance Corp. was pretty much a corporation in name only. They had no offices, property or machinery. So all prototypes and machine work had to be contracted out. For help, Thompson turned to his friends, W.R. Warner and Ambrose Swasey; whom Thompson had come to know from the contracts that their Cleveland, Ohio based machine tool business, the Warner & Swasey Co. had with the Army Ordnance Dept. Warner & Swasey were very interested in the project and provided Thompson with several of their best engineers and machinists. They also provided a testing room in the basement of their plant at 5809 Carneige Ave. (shown on the map). By 1919, Auto Ordnance Corp. would occupy office space in the Meriam building on Euclid Ave., and move it’s operations to a larger machine shop at the Sabin Machine Company, also on Carneige Ave.

By late spring in 1917, work at the Cleveland plant was going full pace. But it wasn't’t long before a series of problems were discovered with the Blish Lock. First, the lock would work fine for several shots, then jam up. Then it was found that under the pressure of high powered rifle ammunition, in a short time abrasion would wear out the lock. Finally, and worst of all, cartridge cases would not extract reliably unless they were lubricated before being chambered. This was an unacceptable requirement for a military firearm that would be expected to function under the most adverse conditions. By September 1917, tests confirmed that the only military service cartridge, currently in use, that would work reliably with the Blish Lock, was the .45 Colt Automatic Pistol Round. Eickhoff dreaded the thought of telling Thompson the bad news.

To Eickhoff’s surprise Thompson took the news very well. Eickhoff remembered Thompson saying “Very well. We shall put aside the rifle for now and instead build a little machine gun. A one-man, hand held machine gun. A trench broom!” Thompson’s comments obviously aimed at the trench warfare being waged in Europe. What Eickhoff didn't know, was that Thompson had already been thinking about the need for such a weapon. The War in Europe was stalled and causalities were mounting. 19th century tactics and 20th century weapons did not mix. The traditional cavalry charge was ineffective against the modern machinegun. But the contemporary machinegun was too large and too heavy to be used offensively. Thompson realized that firepower, and hit and run tactics were what was needed to end the War. He envisioned troops carrying compact machineguns rushing from trench to trench, sweeping the enemy with bullets, while firing at them from the hip. So, under Thompson’s direction, Eickhoff changed the project to work on a class of firearm that never before existed.

By the summer of 1918, all of the major design problems had been resolved. What was left was to address the guns durability and external features. The Annihilator I, as it was code named, was now capable of emptying a 20 rnd magazine in less than a second. Work continued until the fall of 1918, when the final prototypes were completed. Ironically, the first shipment of prototype guns destined for Europe arrived at the docks in New York city on November 11, 1918, the day the War ended. Thompson now faced a huge problem. What do you do with a trench broom, now that the trenches no longer need to be sweeped?

In 1919 Thompson gave Auto Ordnance the task of modifying their new gun for non military use. Eventually the question arose, of what to call it. Thompson wanted something different. Something that would distinguish the weapon from it’s larger bulky machinegun predecessors. They considered the terms “Autogun” and “Machine Pistol”, but finally decided on “Submachine gun” to denote a small, hand-held, fully automatic firearm chambered for pistol ammunition. So, at a meeting of the Auto Ordnance Corp. board of directors, the gun was officially classified as a Submachine gun. And, to honor the man most responsible for it’s creation, the Annihilator was officially named the “Thompson Submachine gun”.

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