The Sten Gun

In our last post, we saw how America adopted the M3 a.k.a the Grease Gun. In today's post, we will look at one of the guns that inspired it, the British Sten gun. This was a gun that was designed to be manufactured cheaply and easily and we will study its origins and design today.

Different Sten gun models. Click on the image to enlarge.

First, we must go back in history to Europe in the summer of 1940. German soldiers were sweeping through Belgium and France and allied troops were in a desperate situation and trapped in the tiny port of Dunkirk. The British deployed every boat and ship available to rescue the stranded Allies and in nine days (27th May - 4th June), over 300,000 soldiers (British, French, Polish, Belgian, Dutch etc.) were evacuated to England. However, this rapid evacuation also resulted in soldiers leaving their equipment behind and large amounts of firearms fell into the hands of the Germans. Shortly after that, the Battle of Britain started and many factories in England were bombed. As a result of all this, there was a shortage of small arms in Britain. The British were buying Thompson submachine guns from the United States, but the factory could not keep up with the demand (and after 1941, many of those Thompsons went to the US military, so they couldn't supply anyone else anyway). Therefore, a decision was made to design a submachine gun that could be made in England quickly and cheaply.

The task of designing this new weapon fell to Major R.V. Shepherd of the Design Department at the Royal Arsenal, Woolich and Mr. Harold J. Turpin, of the Design Department of the Royal Small Arms Factory, Enfield. The design they came up with was called the STEN. The "S" and "T" in the name came from the first letters of the designers last names (S from Shepherd and T from Turpin) and the "EN" came from the first two letters of "Enfield".

From the beginning, the aim was to design a cheap gun that could be manufactured with a minimum of machining operations. It had to be capable of being manufactured in small workshops and produced as quickly as possible. It also had to be capable of single shot and automatic fire and designed for close range fighting. It was designed to use the 9x19 mm. Parabellum Luger cartridge, which was also used by the Germans. The Sten was also deliberately designed to fit German 9 mm. magazines from the MP-38 and MP-40, so that they could use captured German ammunition and equipment if needed.

The design that they came up with was a submachine gun using a blowback mechanism and firing from an open bolt. When the weapon is cocked, the bolt remains at the rear of the weapon. When the trigger is pulled, the bolt is pushed forward by spring pressure and strips a cartridge from the magazine, chambers it and then fires it. The firing pin is fixed in front of the bolt. After the cartridge discharges, the bolt moves rearward against spring pressure and inertia of the heavy bolt and then recocks itself. The working components of this weapon are housed in a basic tubular metal receiver with a barrel on one end and a wire shoulder support welded to the other end, with a simple trigger mechanism in between

The Sten gun, Mark I

The first version of the Sten gun, the Mark I model, came with a conical flash hider and contained some wooden parts (the foregrip and part of the stock). The front pistol grip could also be rotated to make the firearm smaller and therefore, easier to pack. Production started in late 1940 and about 100,000 of this model were made.

Compared to the Mark I model, the Mark II model was much more stripped down. The flash hider was removed and the folding front pistol grip and all the wood were eliminated as well. This made the Mark II smaller and lighter than the Mark I model.

The Mark II variant was the most commonly manufactured model and about 2 million of these were produced. Some Mark II models were made with integral suppressors attached and were classified as Mark II (S)

The Mark III variant was even more stripped down than the Mark II model and was first produced in 1943. In this model, the receiver and the barrel shroud are made from a single tube, by wrapping a sheet steel plate into a cylindrical shape and welding the top. This model is also a bit lighter than the Mark II model.

The Sten Mark III model was the second most commonly produced model of the Sten gun family and was the most stripped down model of the series, and therefore the lightest version.

By 1944, the threat of a German invasion of Britain was over and the Sten gun quality improved. Models Mark IV and Mark V had better quality fit and finish and even came with wooden parts.

The Sten gun model Mark V

The Mark IV model was a paratrooper's model with a folding stock, but never got off the prototype stage. The Mark V model had better sights and finish and came with a bayonet attachment as well.

The Sten was designed to be manufactured quickly and easily. This is why most of the components could be manufactured by stamping sheet metal and doing some minor welding. From the beginning, many of the parts were subcontracted to small workshops, with final assembly being done at the Enfield factory. This was especially useful as the larger factories were being bombed from the air by the German Air Force, early on during the war. The design was made simpler with each generation and the Mark III model only had 47 parts. Interestingly, one of the largest manufacturers of the Mark III model was a toy company called Lines Brothers. The Sten was really cheap to manufacture and only cost about $10 to make, which was much cheaper than the Thompson submachine gun, which cost about $200 then.

While Sten guns were cheap to manufacture, they occasionally had jamming issues as well. The gun was designed to use the same magazine as the German MP-38/MP-40, so that people could reuse captured equipment. However, it also inherited the problems of the German magazine, in particular dirt could cause it to jam. In the absence of a pistol grip and forward grip in the Mark II and Mark III versions, some soldiers would hold the magazine with the supporting hand, causing it to wear out the magazine catch and cause failure to feed issues. The safety device was rudimentary and there was a danger of accidental discharge upon dropping the weapon, especially since many were crudely made. The Mark V model attempted to fix some of these issues.

The Sten was loved and hated by its users at the same time. Many didn't like its peculiar appearance and reliability (at least for the Mark II and Mark III models) and it was nicknamed the "Plumber's Nightmare" and the "Stench Gun". However, they liked its cheap cost and short range firepower. It was manufactured during World War II by many British companies, as well as workshops and factories in Canada, Australia, France, Poland, Denmark, Norway etc. It was responsible for the US manufacturing its own cheap submachine gun model: the M3 grease gun. Towards the end of World War II, even the Germans got in the act and made over 28,000 copies of the Sten gun. After World War II, many were made in small workshops Israel in 1948. The Sten gun is still in use in some countries around the world.

The M3 Grease Gun

In today's post, we will study a submachine gun that was in US service for 50 years and is still used by some military forces elsewhere in the world. Today's post will study about the famous M3 and M3A1 submachine guns, more popularly known as "grease guns".

The origin of this design has to do with the onset of World War II. In Europe, the Germans had developed the MP-40 submachine gun and the British had the Sten submachine gun. Both these weapons were chambered to fire the reliable 9x19 mm. Luger cartridge. In 1941, the US Army Ordnance Board conducted some studies on the effectiveness of these weapons on the battlefield and determined that there was a need for similar weapons for the US military as well. At that time, the US military had already adopted the Thompson submachine guns (which were developed at the end of World War I) into service in 1938, but the Tommy guns were relatively expensive to manufacture. The Ordnance Board wanted a weapon that could fire the same .45 ACP cartridge of the Thompson, but which could be manufactured much cheaper and could be fired as accurately as well.

The final list of requirements included:

1. Weapon to be made of metal completely, with largely sheet metal construction, in order to speed up manufacturing.
2. Weapon designed to fire .45 ACP cartridges, since the US military was already using this cartridge (The Germans and British were using 9 mm. Luger cartridges for their submachine guns)
3. Weapon to be designed for fast production, with a minimum of machining operations.
4. Weapon to be designed to be cheap to manufacture (cheaper than the Thompson submachine gun)
5. Weapon to be designed as reasonably accurate. It was required to demonstrate that this weapon could put 90% of shots fired in a standing position in full-automatic mode into a 6x6 foot target at a distance of 50 yards. 
6. Weapon to be capable of firing in both semi-automatic and full-automatic modes. This requirement was later removed during development of the weapon and it was designed to fire full automatic only.

The task of designing this weapon fell to George Hyde of General Motors' Inland Division. George Hyde was actually of German descent and had emigrated to the US in 1927, whereupon he changed the spelling of his last name from "Heide" to "Hyde". He was a well known gun designer in 1941 and was put in charge of designing the new weapon. Meanwhile, another engineer named Frederick Sampson was put in charge of preparing the tooling for mass production of this weapon. During the design phase, a conversion kit was also designed, which would allow the user to quickly convert the gun from firing .45 ACP to firing the 9 mm. Luger cartridge.

The prototypes were completed in late 1942 and approved for mass production. The Guide Lamp division of General Motors (the same people that manufactured the FP-45 Liberator pistol) was put in charge of manufacturing it. While the weapon was given the official designation of "U.S. Submachine Gun, Caliber .45, M3", many people noticed that it resembled grease guns used by automobile mechanics and therefore, the new weapon was nicknamed the "Grease Gun".

The M3 Grease Gun. Click on the image to enlarge.

Image licensed under the Creative Commons Share-Alike 3.0 Unported license by Curiosandrelics

The M3 was designed to be cheap. The manufacturing cost of one of these in World War II was around $18. Only three parts, the bolt, the barrel and the firing mechanism, were precisely machined. Most of the other parts of this gun were manufactured by using metal stamping and pressing technologies. Spot welding and seam welding were used to join most of the parts together and some other parts were riveted together. These processes allowed the gun to be manufactured very rapidly and with low cost. The stock was simply made from a single steel rod, which was bent into shape. The ends of the stock were drilled and tapped, so that it could be used as a cleaning rod, as well as a disassembly tool. In the M3A1 model, the stock also had a tool welded to it, to be used to load a magazine. The safety was a projection on the inside of the ejection port dust cover, which locked the bolt into the forward or rear positions. However, since the metal around the dust cover was so thin, it could get bent easily and the safety mechanism wouldn't work any more.

The two halves of the receiver were made by stamping sheet steel and then the two halves were welded together. The bolt was made heavy and made to run on two parallel guide rods, which had twin return springs. This allowed the receiver to be made to looser tolerances. The barrel was cold swaged to save time and cost. The weapon was designed to be striker fired, with a fixed firing pin inside the bolt.

When the M3 first entered service, no replacement parts were supplied. The weapon was originally intended to be a low-cost tool that could be discarded when it ceased working. However, due to a temporary shortage of M3s in the middle of 1944, the US Army Ordnance workshops manufactured some spare parts to keep existing weapons operational. There were also a number of issues with the M3 and several improvements were incorporated into the M3A1 model, which went into service in December 1944. During the Korean war, existing M3 guns were converted to the M3A1 standard.

While it was hoped that this gun would be produced in large numbers to replace the Thompson submachine gun in US service, this did not happen and there were about three times as many Tommy guns in service than M3/M3A1 at the end of World War II.

Due to its cheap cost and portability of the weapon, it was issued to paratroopers, tank crews and truck drivers. Even though it was withdrawn from frontline service in the US military in 1957, they were still issued to tank and truck drivers and were carried by US tanks during the 1991 Gulf war. The M3A1s were finally replaced starting in 1992, with the M4 carbine. That means it served in the US military for 50 years (1942 - 1992). It is still used by military forces in other parts of the world.

History and Development of the Assault Rifle - II

When World War I started, the French introduced a light machine gun called the Chauchat. While it was capable of selecting both single and automatic firing modes, this firearm used full sized cartridges, unlike an assault rifle. It was also a notoriously unreliable weapon, because it did not function well under muddy conditions and jammed frequently because the slots cut into the magazine would let in dirt and mud. The .30-06 version also frequently jammed after a few shots once the gun became hot. In fact, it has the dubious distinction of being dubbed "worst machine gun ever" by several firearms experts. Still, it was not only used by the French, but also other allies such as Belgium and the United States. Captured Chauchats were even used by the Germans because they didn't have any comparable automatic firearms.

Chauchat Machine Gun. Click on image to enlarge.

Due to the Chauchat's unreliability under battlefield conditions, US troops turned to the redoubtable John Browning for help and he delivered the M1918 Browning Automatic Rifle (BAR) design in 1918. This weapon was introduced rather late in the war, but was very effective when it was used during this short time. The first time it was used was September 13th 1918 and one of the people demonstrating its use against the enemy was John Browning's son, Val Allen Browning.

Browning Automatic Rifle. Click on image to enlarge. Public domain image.

The BAR was so successful that the French ordered 15,000 of them to replace their own Chauchats! The BAR remained in production until the 1950s.

Note that both the Chauchat and BAR use full-size rifle cartridges. There were also automatic weapons designed during World War I, that used pistol ammunition. The most famous of these was the Thompson submachine gun, the so called "Tommy gun" that we studied about previously, when we studied the Blish lock mechanism. Both the Tommy gun and the BAR were designed rather late in the war though and the Tommy gun never saw action in World War I, but saw plenty of action in the hands of mobsters.

During the peace time period of World War I, several people argued for a new intermediate cartridge that was smaller than existing rifle cartridges, but bigger than pistol cartridges, and a suitable weapon to fire this new cartridge. The Swiss designer Furrer made an intermediate 7.65x35 cartridge for a carbine in 1921 and one Hauptmann Piderit of the German Rifle Testing Commission also advocated a shorter cartridge and a rifle to fire it. Colonel Fedorov, who we studied in the previous post, was also arguing for a smaller cartridge. There were also experiments made in Denmark and the US.

It was however, Germany, where some of the major new development took place. The Germans had observed that a small group of soldiers could easily overcome a larger group, provided that they had superior firepower. It was also observed that most infantry combat happened at less than 400 meters or so. By the 1930s, at least 5 German companies (Geco, DWM, RWS, Rheinmetall and Polte Patronenfabrik) were experimenting with intermediate rifle cartridges. It was Polte that was officially awarded the contract to design a new intermediate cartridge by the German military and after some experiments, came out with the 7.92x33 mm. "kurz" (German for "short") cartridge in 1938.

Contracts to design a new rifle for this cartridge were sent to both Walther and Haenel GmbH. Haenel's chief designer was Hugo Schmeisser and his design won out over the Walther design and was designated as the Maschinenkarabiner 1942 (after 1942, the year it was adopted) or MKb 42 for short. It underwent some minor design modifications, as requested by the German military. The Haenel design originally used an open bolt mechanism, but after a few trials, it was requested to make a closed bolt design similar to the Walther entry.

As it turned out, Adolf Hitler was strongly opposed to the new intermediate cartridge and demanded that more submachine guns be built instead. However, the German armament office secretly kept working on this new firearm and to avoid raising suspicions, they christened the weapon as MP 43 (MP = Machine Pistol). Hitler later asked for it to be renamed the MP 44, after some official tests in April 1944, unaware that it was not a machine pistol at all. In July 1944, Hitler held a conference with his generals on the Eastern Front and asked them what they needed most. A general who had no idea that the German armament office had disobeyed Hitler's orders, replied, "We want more of those new rifles!" and a thoroughly confused Hitler asked, "What new rifles?" and the cat was out of the bag. Some people thought they would be executed for disobeying Hitler's direct orders, but once Hitler was given a chance to test-fire the new MP 44 for himself, he became very impressed and enthusiastically gave it the name Sturmgewehr, which is German for "Storm (Assault) Rifle" ("Storm" as in storming a castle or assaulting a castle). This is where the term "Assault Rifle" comes from. Because of this new official name, the MP 44 was rechristened the StG 44.

Sturmgewehr 44 (StG 44), the first firearm to be called "Assault Rifle". Click on image to enlarge. Public domain image.

The StG 44 was heavily used in the Eastern Front and found extremely useful by soldiers. It was also very reliable in the extreme cold conditions of the Russian winter. It had a longer range than the Russian submachine guns, but a comparable rate of fire, switchable firing mode from single shot to full automatic mode, pretty decent accuracy and decent controllability even in fully automatic mode.

The StG 44 is now generally accepted as the world's first successful mass produced assault rifle. It was an encounter with one of these that prompted a Russian tank mechanic to invent his own assault rifle, which would later become one of the most famous designs world wide. But that is the subject of another article.

Actions: Blowback Action: Blish Lock

In our last few of posts, we've studied the basic principles of a blowback action and the reason why we want to delay the blowback action. In our last couple of posts, we saw that mechanical means can be used to delay the movement of the bolt. In this post, we will look at another way to delay the movement of the bolt -- a method that uses static friction, the so-called Blish lock. The Blish lock is used in one of the most famous weapons invented in the early 20th century, the weapon that gave rise to the term "submachine gun", the one and only Thompson submachine gun, a.k.a the "tommy gun".

The Blish lock was invented by John Bell Blish, a career officer in the US Navy. While he was serving aboard a US Navy warship, he noticed a very interesting fact about naval guns. The guns in question were breech loading with screw on type breech blocks. He noticed that if a gun was fired with a normal round with a full load of gunpowder, the breech block would hold in place perfectly, but if it was fired with a training round which has a lot less gunpowder in it, the breech block would tend to unscrew itself and the case would fall out. After a lot of analysis about this phenomenon, he came to the conclusion that certain dissimilar metals tend to stick to each other if very high pressure is applied. This principle of metal-to-metal adhesion is now known as the "Blish principle." This adhesive force is really due to static friction between the two metallic surfaces. While he was not entirely certain about the physics behind the phenomenon, he did nevertheless note down that it happened and applied it to designing a wedge shaped blowback action that he patented in 1915. The action consisted of two diagonally sliding dissimilar metal wedges on the back of the bolt. Due to the pressure of the gases and the Blish principle, these two metals would adhere to each other initially. This extra resistance slows down the backward movement of the bolt. It was noticed much later that the Blish lock was not as effective as proclaimed, and the same effect could be obtained by merely increasing the weight of the bolt by one ounce and making it work on the principle of straight blowback.

While the Blish lock patent itself went nowhere initially, the next development came due to a retired US Army General, John T. Thompson, and the onset of World War I. The standard US military rifle at that time was the venerable bolt action M1903 Springfield rifle and the standard pistol was the Colt M1911. Interestingly, Gen. Thompson had earlier served as the chief of the Small Arms Division of the Ordinance department and had supervised the development of the Springfield M1903 rifle and approved the selection of the Colt M1911 pistol.

During World War I, trench warfare became the standard method of fighting and it became clear that there was a need for a weapon with a high rate of fire that could be used to clear a trench of enemies. General Thompson was looking to replace the bolt action rifle with an auto-loading one, a concept he called the "trench broom." He was aware of gas operated and recoil operated actions in his day, as these were in use for medium and heavy machine guns, but these used many heavy moving parts and were not as reliable then. He researched the straight blowback actions of the day, which were only suitable for really low powered ammunition. While he was studying various blowback actions, he came across the Blish patent and decided to use it instead. Accordingly, he arranged a meeting with John Blish and offered him some stock in the new weapons company he was planning to form, in exchange for the manufacturing rights of the Blish patent.

With Blish as a partner, Thompson secured some venture capital and formed the Auto-Ordnance Corporation in 1916. He also managed to hire Theodore Eickoff, who was once Thompson's assistant when he was running the Army Ordnance department. He also found an unemployed railroad fireman with mechanical aptitude called George E. Goll and hired him to be Eickoff's assistant. These two men were the principal designers of the Thompson submachine gun. Later on, Oscar Payne also joined and added some key Tommy gun features, such as the self-oiling mechanism and its distinctive drum magazine.

The original plan was to develop an auto-loading rifle using the military .30-06 round, which is the same round that the Springfield M1903 rifle uses. However, a series of problems were discovered with the Blish lock. For one, it could not handle such a powerful round and would wear out prematurely. Worse, the extraction of the fired cartridge case would not work unless the cartridges were lubricated. Eickoff did some research and found that the only military cartridge that would work reliably with the Blish lock was the .45 ACP cartridge, which is the cartridge used for the Colt M1911 pistol. Eickoff dreaded telling Thompson the bad news, but to his surprise, Thompson took the news very well and said "Very well, we will put aside the rifle for now and instead build a little machine gun. A one-man, hand held machine gun. A trench broom!" Thompson had realized what many European generals of the era hadn't, that nineteenth century warfare tactics didn't mix very well with twentieth century weapons. The traditional cavalry offensive charge was no match for heavy machine guns in trenches and the war had stalled with heavy casualties and little progress. While machine guns of the day were great for defense, they were too large and too heavy to be used for offensive actions. What Thompson visualized was a hand-held weapon with enough firepower, that could be used for hit-and-run tactics to clear enemy trenches. Accordingly, he directed Eickoff to develop a class of firearms that had never existed before then.

By the summer of 1918, all problems had been solved and the new class of weapon was called the "Annhilator Mark I". The first batch of weapons destined for Europe was delivered to the New York harbor on November 11th 1918, the very day that the armstice was signed in Europe, signalling the end of World War I. Suddenly, Thompson was stuck with a weapon that didn't have any demand! However, he was not a man to be let down by this setback and directed Auto Ordnance to redesign it for civilian use, which they did by 1919. Seeking a new name that could be used to distinguish it from its larger and heavier machine gun ancestors, he came up with names like "Autogun" and "Machine pistol", before coining the term "submachine gun". The rest, as they say, is history.

Two views of the Blish lock (note the brass content). Note the wedges along the center and the sides of the H shaped lock.

Bolt, Blish lock and actuator of a Tommy Gun. Note the dissimilar metals used

Disassembled Blish Lock, Bolt and Actuator

Tommy Gun with straight box magazine

Tommy Gun with rotary drum magazine

The Tommy gun was initially marketed to the police. The improved model M1921 was also offered for sale to the general public. It was a very finely machined weapon with high quality components and consequently commanded a high sale price of $200 (for contrast, a Ford car of that era cost only $400). It really came into the public eye during the Prohibition era, when both gangsters and law enforcement began to heavily use it. It acquired such nicknames as the "Tommy Gun", "Chicago Piano", "Typewriter", "Chicago Typewriter", "Chopper", "Broom" etc. Due to its notoriety, it was the main reason for the passage of the National Firearms Act of 1934 in the US. It was also used by the US marines in several smaller conflict and was adopted by the US military in 1938. It was used in World War II, Korea, Vietnam and beyond. It still turns up in some present day conflicts occasionally, such as the Bosnian war of the 1990s.