The Vickers Mk.I: Origins and Technical Evolution
At the turn of the 19th and 20th centuries, English small arms were considered among the most advanced. However, during World War I, the national conservatism characteristic of the British began to manifest in the development of new, advanced designs. It cannot be said that English rifles and machine guns were fundamentally worse than French, German, or American ones, but in terms of creating something fundamentally new and revolutionary, the British lagged somewhat behind other countries, only improving and perfecting foreign innovations.
In the field of aviation small arms, this thesis was no exception. Although, in fairness, it should be noted that during World War I, British gunsmiths were among the first to test cannon armament in the air and developed a large amount of useful peripheral equipment for aviation armament, including the disintegrating machine gun belt, the hydraulic synchronizer, and the defensive turret—the so-called “Scarff Ring.” But the machine guns themselves, primarily the reliable, trouble-free Vickers Mk.I, essentially a refined “Maxim,” were the fruits of foreign developments.
In the 1920s and 1930s, the “Vickers-Armstrong” concern became the monopolist in machine gun armament, perfecting successful designs from the beginning of the century. As is typical of any monopoly, over time, stagnation set in, caused by complacency. As a result, in the field of small-arms and cannon aviation armament, the British simply missed the revolution in aviation when, in the second half of the 1930s, they suddenly realized that rifle-caliber “Vickers” machine guns had simply lost all meaning.
The British did not have time to quickly develop more effective weapon systems. The only new development—the “Vickers GO” or “Class K” machine gun—was obsolete before it was born. Attempts to create large-caliber machine guns for the RAF based on the same proven “Vickers” design from the beginning of the century did not lead to satisfactory results. Before World War II, the British had not even begun to develop automatic cannons of their own design. The outcome of all the above was that by September 1939, British aviation would have been practically unarmed if it had not arranged for licensed purchases. And in the battles of the Battle of Britain, British aircraft participated almost 100% armed with overseas Brownings, to which French Hispano cannons were later added.
At the very beginning of the 20th century, the British corporation Vickers bought the patents of the American engineer Hiram Maxim, and, perfecting the basic design of the Maxim machine gun, set about improving it. As a result of the work of Vickers engineers, in 1911 the British Army adopted the Vickers Mk.I machine gun of .303 caliber. Its main visual distinction from the “original” Maxim machine guns was a smaller height of the receiver, and consequently, a lighter weapon. This was achieved by changing the direction of the “folding” of the toggle lock mechanism, which locked the bolt—in the new Vickers, it folded upwards, not downwards. The machine gun received several other minor improvements, and in this form, it managed to set one of the longevity records, remaining in service with the British Army until the mid-1960s, which is more than half a century, when it was replaced by the L7GPMG (FN MAG) general-purpose machine gun. The Vickers Mk.I machine gun is an automatic weapon with water cooling of the barrel. The machine gun’s automation uses barrel recoil in its short stroke. For anti-aircraft and aviation variants of the machine gun, a special muzzle device—a recoil accelerator—was sometimes used. This device utilized the pressure of propellant gases at the muzzle to increase recoil energy, thereby increasing the rate of fire. The barrel is locked by a toggle-joint system of levers, located between the bolt and the receiver rigidly connected to the barrel. The machine gun only allowed automatic fire. Firing was conducted from a closed bolt. Ammunition is supplied from a canvas belt, fed only from the right side of the weapon.
Aviation Integration and Synchronization Breakthroughs
In the first months of 1916, the British Air Force made the first attempt to adapt the standard army Vickers Mk.I machine gun for use in aviation. Until then, aircraft were mostly just flying platforms, with the weapons mounted on them controlled by a separate crew member. The aircraft’s propeller was an insurmountable barrier to mounting weapons for firing strictly forward. The famous French ace pilot Roland Garros tried to solve this problem by mounting a machine gun on a stand, above the plane of the propeller. However, this setup only allowed firing while standing, distracting the pilot from controlling the aircraft. There was also a solution to mount the machine gun on the upper wing of biplane fighters of the time with a remote cable trigger device. However, even in this case, to reload the machine gun, the pilot had to stand up in the aircraft cockpit, which was both inconvenient and unsafe. Later, the Foster device was developed, which allowed the machine gun to be pulled down for reloading, which, incidentally, also allowed the machine gun to fire not just strictly forward.
Some brave individuals risked firing the machine gun directly through the propeller disk, hoping that a couple of bullet holes in the wooden propeller blades would not severely damage it. An analysis conducted at the end of 1914 showed that only 2 percent of fired bullets hit the propeller blades, which was relatively safe for the blades’ strength. As a result, it was decided to install one machine gun directly in front of the propeller disk for emergency use. However, practice showed that every pilot considered any encounter with an enemy aircraft an emergency and used this machine gun in any case. This, accordingly, led to the predictable result of numerous accidents and disasters, when English pilots shot off their own propeller blades.
In 1915, the French proposed installing the machine gun in front of the cockpit and equipping the propeller blades with steel deflectors that protected the propeller from through-shots. But all this was only half-measures, and thus, in the early stage of the war, machine guns installed on aircraft were of little use, and their application in the aerial combat of 1914 was very limited. From the very beginning of the war, intensive work was carried out to adapt the Vickers machine gun for use on aircraft. First, attempts were made to reduce the weight of the machine gun, which weighed over 18 kilograms. Primarily, the massive water cooling jacket was eliminated, replaced by a finned air radiator covered by a lightweight perforated casing, which immediately reduced the machine gun’s weight from 13.6 kg (and with water in the radiator, 18.2 kg) to 11.4 kg. The belt feed was also modernized, which was the most radical change.
Now, the belt could be fed from both the right and left sides, allowing two machine guns to be mounted next to each other. In addition, a handle was added to adjust the tension of the return spring. This variant of the machine gun, designated Vickers Mk.II, was used to a limited extent in British aviation at the end of World War I. One of the most important improvements to the Vickers machine gun was the invention of the muzzle booster, which consisted of a cup installed on the muzzle with a hole for the bullet to pass through. As the bullet exited the barrel, it passed through the cup, and the propellant gases, expanding instantly in this cup, acted on the barrel’s end and pushed it backward, increasing the rate of fire. This required reinforcing the buffer to absorb the excessively powerful recoil.
The authorship of the muzzle booster invention is still disputed, as similar devices were almost simultaneously designed by Lieutenant Commander George Hazelton of the British Royal Navy and Lieutenant Viktor Vasilievich Dibovsky of the Russian Imperial Fleet. The use of muzzle boosters allowed the practical rate of fire to be increased from 540 rounds/min to 1000. However, despite the excellent characteristics of the Vickers machine guns, at first, English pilots preferred the more convenient “Lewis” with its easily replaceable drum magazine, designed by American Army Colonel Isaac N. Lewis. As mentioned above, in the initial period of World War I, the use of machine guns firing strictly forward in the aviation of the Entente countries proved to be quite complex. The Germans, who were the first to use a synchronizer developed before the war, gained a real advantage. The system for synchronizing machine gun fire with propeller rotation ultimately amounted to a series of single shots, significantly reducing the rate of fire, which varied depending on the propeller speed. To ensure this, each shot from the machine gun had to be fired strictly at a specific time. But, alas, the “Lewis” machine gun, so popular in England, was incapable of this.
The design of the Lewis machine gun operated on the principle of an open bolt, where its design elements were not connected to the fixed barrel. The movement of the bolt occurred only due to gas energy, so each time a signal was received from the synchronizer to begin firing, the bolt had to go through a rather long cycle: moving forward, grasping a cartridge from the magazine, chambering it, firing, and with the reverse movement, ejecting the spent casing. During this time, the propeller blade had time to pass the machine gun barrel. Despite numerous attempts to change the design of the “Lewis” machine gun, it was never reliably adjusted to work with a synchronizer. The operating principle of the “Vickers” machine gun, however, was based on automatic action with barrel recoil (short stroke). As a shot is fired, propellant gases send the barrel backward, which initiates the reloading mechanism—it extracts a cartridge from the fabric ammunition belt, chambers it, and simultaneously cocks the bolt. After the shot is fired, the operation repeats, meaning the cartridge is already in the chamber before each shot. This scheme was ideally suited for synchronization. Additionally, the machine gun featured a belt-feed system with a capacity of 250 rounds, thereby freeing the pilot from the problems of changing magazines in flight.
Many engineers from the Entente countries attempted to create an aviation synchronizer, but these were mostly mechanical devices, kinematically linked to the engine shaft by a set of levers and rods. Such devices required high manufacturing precision and constant adjustment. Moreover, they too often failed during combat operations. The revolution in this direction was accomplished by the Romanian engineer George Constantinesco, who lived in London. He was the first to discard the idea of a mechanical synchronizer drive, applying hydraulics. The essence of the idea was to transmit an impulse from the engine shaft to the piston of an oil hydraulic cylinder, which, at the same time, was connected to the machine gun’s sear. Each time the propeller blade reached a certain position, the piston acted on the machine gun’s sear, interrupting fire, and resuming it as soon as the blade passed the firing zone. Thus, all mechanical synchronizers instantly became obsolete. In August 1916, BE2C aircraft equipped with Constantinesco synchronizers successfully passed trials. And in March 1917, the first squadrons of DH-4 bombers were already participating in combat. By the end of the war, about 26,000 British aircraft were equipped with them.
Global Adoption and Ammunition Developments
Thus, from the summer of 1917, Vickers machine guns, models Mk.I, and from early 1917, the lighter Mk.II with air cooling instead of water, became the standard synchronized offensive armament for RFC aircraft. The Vickers Mk.II machine gun, as a fixed offensive weapon, had practically supplanted all other machine gun models in service with British aviation by the end of the war. Thus, the “Vickers” Mk.II, introduced into service in 1917, became the standard offensive weapon for British army and navy aircraft. By the 1920s, it was replaced by a somewhat modernized “Vickers” Mk.III, in which muzzle boosters became standard, and then the “Vickers” Mk.V with two-sided belt feed. As an offensive weapon, it was in service with RFC, and later RAF, fighters and bombers until the late 1930s and saw the beginning of World War II on obsolete “second-line” aircraft, such as the Hawker “Fury”; Gloster “Gladiator” and the family of Hawker multipurpose biplanes “Audax”/”Hart”/”Demon”/”Hardy”/”Hind,” of which there were many in service with British colonial troops scattered across all continents. The “Vickers” Mk.II, Mk.III, and Mk.V machine guns, which also had the general export name “Vickers Class E,” were the main synchronized offensive armament in Great Britain, the Dominions, and many other countries where they were sold or built under license in the 1920s and 1930s. However, “Lewis” machine guns were still preferred by turret gunners.
In the early 1920s, the “Vickers” design underwent some changes for use by bomber gunners, mainly for export supplies. The automatic mechanism of the machine gun did not change, but two grips and a trigger guard were introduced. The intermediate “Vickers” Mk.III model was taken as the base. Belt-fed ammunition was replaced by a 97-round drum magazine. The machine gun, in fact, was not intended for arming British aviation, having been developed for a Polish order. The version received the export designation “Vickers Class F.” But it proved to be quite successful and was adopted by the RAF, becoming for a short period the basis of defensive armament for turret and pintle-mounted gunners; however, by the beginning of World War II, it had not fully displaced “Lewis” machine guns from RAF units. In addition to England, Class E and F machine guns were in service with a large number of countries. In the Netherlands, Poland, and Czechoslovakia in the 1920s, these machine guns were re-chambered for the 7.92×57 cartridge. The Czechs produced a deeply modified version of the machine gun under the designation CZ vz.30 in a turret version with a 50-round drum magazine and a synchronized version with belt feed for 250 and 450 rounds. Approximately 4,500 machine guns of both versions were produced at the Ceskoslovenská zbrojovka Brno factory. This type of machine gun was in service with all Czech aviation in the second half of the 1930s. Inherited by the Germans, they were renamed MG 30(t) and used by Czechoslovakia’s new masters during World War II.
Japanese army and naval aviation virtually from their inception used various modifications of Vickers machine guns as armament. Reliable, well-proven, and unpretentious, they were purchased in large quantities from Great Britain until the late 1920s under the designation “Type BI,” when Japanese army officials arranged for the purchase of a license for machine gun production. Licenses were acquired for the serial production of two types: “Vickers” Class E—a fixed variant with belt feed, and “Vickers” Class F—a variant for mobile mounts with a drum magazine. The Class E was produced from 1929 under the designation “Type 89 fixed.” Two models of the Type 89 machine gun were distinguished. Model 1—for the English cartridge and its slightly modified Japanese analog 7.7×58 Type 89, and the more common Model 2 for the new “semi-rimmed” machine gun cartridge 7.7x58SR Type 92. The “Type 89” machine gun became the basis of the offensive armament of Japanese army aviation for the next 13 years, being used on almost all army aircraft of the 1930s. The turret “Vickers” Class F was adopted with some design changes. Under the designation Te-1, the turret Vickers was produced with both belt feed and a 69-round drum magazine, but it was used very limitedly in aviation.
Japanese naval aviation, traditionally abstracting itself from its army counterparts, long relied on purchased Vickers. Only in 1937 did they arrange for a license to produce the fixed “Vickers” Class E model, which under the designation Type 97 was manufactured by the “Nihon Seikoujo” company, as well as at the naval arsenals in Yokosuka and Suzuka, practically until the end of World War II. Unlike their army counterparts, the sailors did not adapt the English machine gun to their cartridges, using the English licensed “0.303 British” 7.7x56R. The Japanese naval Vickers—Type 97—became the main offensive armament of Japanese naval fighters and bombers in the late 1930s, remaining in service until the end of the war. The machine gun’s automation worked on the principle of short-recoil. Air-cooled, the machine gun weighed 11.4 – 11.8 kg. The rate of fire varied depending on the diameter of the hole in the muzzle booster cup and the power of the buffer accelerator springs. The normal rate was 540 rounds per minute. The rate with one accelerator was 750 rounds per minute, with two – 960. Usually, the machine gun was used with only one accelerator, as the rate of 960 rounds could not be sustained by the machine gun for long. The initial bullet velocity was 775 m/sec.
The movable system of the machine gun consists of the barrel, frame, connecting rod with crank, and lock. At the moment of firing, gases through the cartridge case push on the lock, but cannot throw it back, as the crank with the connecting rod rests against the frame protrusions and forms an obtuse angle. The recoil is transmitted to the crank axle, and the movable system moves backward. As the bullet exits, gases additionally push on the barrel muzzle and accelerate the backward movement of the movable system. As it moves backward, the movable system stretches the return spring, winding a chain onto the drum. The handle slides onto a roller and rotates with the crank axle. The crank lowers and pulls the connecting rod. The lock, not held by the connecting rod, moves away from the barrel, extracting a cartridge from the receiver and a casing from the chamber. The barrel, along with the barrel frame, having reached its extreme rear position, returns to its original position under the action of the spring, but the lock continues to move backward by inertia, stretching the return spring. Upon impact of the short arm of the handle on the roller, the return spring sends the lock to the forward position. The lock face chambers a new cartridge into the chamber, which is cleared of the fired casing, sending it to the ejection window, and with its claws grabs the next cartridge in the longitudinal window of the receiver. The lock, along with the lever system, tightly locks the chamber for the next shot. When the frame moves forward, the receiver’s lever and slider are activated, moving the belt to feed the next cartridge to the longitudinal window. The fabric machine gun belts used in Vickers machine guns during World War I had the disadvantage that the empty belt, exiting the machine gun, flapped in the wind, got wet, and froze in winter. In 1917, the French civil engineer William de Courcey Prideaux, who was then residing in Great Britain, proposed replacing the canvas cartridge belt with a metal disintegrating link belt, where each link was connected to the subsequent cartridge. The beauty of such an ammunition system was that all Vickers machine guns could be modified by changing two small parts in the belt receiver. Immediately after the end of the war, this ammunition system was adopted in Great Britain, and from there it migrated to all countries, being an integral part of virtually all automatic weapon systems from rifle caliber to 40mm “Bofors” automatic cannons. It is quite difficult to accurately estimate the total number of rifle-caliber Vickers machine guns produced. Only infantry variants from 1913 to 1947 saw about 150,000 units produced in Great Britain and Australia. Under subcontracting agreements, machine guns were also produced in the USA and Canada during World War I and II. Under license, “Vickers” was produced in Japan. So the total number of “Vickers” machine guns of all rifle-caliber versions (not counting the later “Vickers-GO”) can be estimated at no less than half a million units.
From the moment machine gun armament appeared on aircraft, the issue of cartridge quality became very acute. An infantryman could always discard a defective cartridge, but in the air, this represented a considerable problem on which the pilot’s life depended. In an attempt to solve this problem, in 1917, the British introduced a system of markings for .303″ rifle cartridges on ammunition production lines. Thus, “Green Marking” (or “Green Cross”) meant that the ammunition was specially intended for synchronized fighter machine guns. These were individually selected from batches produced to tighter tolerances on standard production lines. The initiative was successful, and in 1918, new lines for producing ammunition for the royal air force began to be created at armaments factories. Ammunition marked with “Red Marking” was labeled on cartridge boxes as “Special for RAF, Red Label,” meaning specifically for the Royal Air Force. The second task facing the RAF was the need to equip cartridges with special bullets, which was initially caused by the necessity of combating hydrogen-filled German Zeppelins, which were insensitive to ordinary bullet perforations. Several attempts were made to develop bullets filled with various explosive and/or incendiary compositions. Initially, work was carried out on larger caliber ammunition, but soon the English industry also became fully engaged in standard .303″ caliber cartridges. Some types of incendiary ammunition, such as the “Buckingham” cartridge, whose bullets contained a mixture of phosphorus and aluminum powder, ignited immediately after leaving the barrel and burned, leaving a characteristic smoky trail throughout the flight to the target. Others ignited on impact.
A prominent representative of this ammunition was the so-called “Pomeroy” (Pomeroy) or “PSA,” with an explosive bullet filled with nitroglycerin, whose disadvantage was its extreme explosiveness; Brock bullets were filled with potassium chlorate, and “RTS” – “Richard Threlfall and Sons” were filled with nitroglycerin and phosphorus, possessing both incendiary and explosive properties and were called high explosive-incendiary (HEI). The British aviation cartridges from World War I shown in the photograph in cross-section are characterized by the shot charge. The first three cartridges were loaded with cordite in the form of extruded cords; the last, the Threlfall cartridge, was loaded with nitroglycerin powder. The use of these bullets was initially quite dangerous, as early versions had a reputation for premature detonation and also required special safety measures for their storage and use. These bullets were initially reserved for metropolitan defense, partly because they were needed to combat German airships during their raids on English cities. And partly due to fears of their illegality—explosive and incendiary ammunition was prohibited by international agreement as inhumane. Nevertheless, they were used by both warring parties, and after the war, it was recognized that they were acceptable as they were intended for use against aircraft, not people.
The imperfection of early aircraft sights led to the appearance of tracer bullets, very useful for adjusting fire at moving targets. The bullets were loaded with a combustible mixture that ignited the moment the bullet left the barrel and burned during its flight to the target. The mixture consisted of barium oxide, a very strong oxidizer, combined with powdered magnesium, a substance that burns with a highly visible flame. Tracer ammunition not only allowed the pilot or gunner to correct fire but also, in many cases, served as incendiary, especially in combating hydrogen-filled German airships. By the beginning of World War II, considerable work had been done in the United Kingdom on the development and modernization of standard .303-inch aviation ammunition. Armor-piercing bullets with a steel core and the “Buckingham” cartridge with an incendiary-tracer bullet (designated B. Mk.IV) were based on old designs, but there were also new munitions. For example, the B. Mk.VI incendiary, developed by Major Dixon, based on the Belgian De Wilde design. During tests of the new cartridges, the B. Mk VI proved to be 20% more effective than the “Buckingham” cartridge or the German 7.92 mm in terms of the probability of igniting an enemy aircraft’s fuel tank. Additional benefits were also noted, such as clearly visible flashes on impact, which could be convenient for a fighter pilot to confirm a hit on the target. Subsequently, the Americans adopted the design of Dixon’s cartridges and launched them into production in a simplified form for their .30 and .50 inch incendiary ammunition, and the British, in turn, copied the simplified American version as B.Mk VII.
Unlike the practice in other countries’ air forces, where mixed combat loads of different ammunition types were used when loading machine guns, the RAF preferred to load 7.7mm fighter machine guns with only one type of ammunition. Dixon cartridges were first used in June 1940 and were initially in short supply. Originally, in “Hurricane” and “Spitfire” fighters, one machine gun was loaded with Dixon incendiary cartridges, two with “Buckingham” incendiary, two with armor-piercing, and three with ordinary, full metal jacket lead bullets. By 1942, the standard load for 7.7mm fighter machine guns consisted of an equal number of machine guns loaded with armor-piercing and incendiary cartridges.