Steam Chests

A few posts ago, when we studied heavy machine guns, it was mentioned that one of the features of some of these machine guns is a jacket filled with water, which surrounds the barrel and helps to prevent it from overheating.

Of course, if several rounds were to be fired rapidly, the intense heat of the barrel would cause the water to turn into steam and evaporate, thereby reducing the cooling effectiveness of the jacket. In the early Maxim heavy machine guns, the users would simply unscrew a cap on the top of the water jacket and refill it with more water, whenever the water level in the jacket got low.

A Maxim machine gun. Click on the image to enlarge.

Image licensed under the Creative Commons Attribution-Share Alike 3.0 License by Jonathan Cardy at Wikipedia

However, this presented a logistical problem to its users because then they needed to position the heavy machine gun next to a supply of water and this was not always possible in the battlefield. Resourceful users found that they could urinate into the water jacket in an emergency, but it is not possible to do that on demand, therefore it is preferable that a reliable supply of water be nearby. Another problem was that the steam rising from the barrel could also give away the position of the machine gun. This was a problem in trenches and rough terrain, since heavy machine guns cannot be moved as quickly by troops without a vehicle. Another issue was that if the steam was not allowed to escape out of the water jacket, the steam pressure inside could build up to the point of rupturing the jacket.

To counter these issues, newer models of heavy machine guns at the end of World War I were issued with steam chests. A steam chest, or more properly, a steam condensing chest, is simply a container that is placed below the barrel and is connected to the water jacket via a short pipe (or pipes). When steam is created by the hot barrel, instead of allowing the steam to escape out of the water jacket, it is transported through the pipe into the steam chest, where it condenses back into water. Periodically, this water is poured back into the water jacket for reuse. This system allows users to conserve their water supply for much longer and also prevents steam from rising and revealing their position to enemies.

A Browing M1917A1 machine gun. Note the steam chest attached to the front of the water jacket.

In the above image, we see a Browning M1917A1 machine gun. The steam condensing chest is the rectangular can at the front with the rubber hose coming out of it. The steam coming out of the water jacket flows through the rubber tube (which has some water in it as well) and into the rectangular can, where it cools down enough to become water again. Periodically, the crew lifts the can above the height of the water jacket, which causes the water in the can to flow back through the tube into the water jacket.

In the above image, note that the can is a custom made device with its own folding carrying handle. However, any convenient container could be used as well, as the image below shows:

A British Vickers machine gun with its condensing chest. Click on the image to enlarge. Public domain image.

In the above example, we see a Vickers machine gun, as used by the British military. The steam chest on the right of the picture has some faint lettering on it, which may be discerned by clicking on the image to enlarge it. Still having trouble reading the letters?? The image below shows a closeup of the steam chest with the letters clearly visible:

A can of Shell gasoline! Public domain image. Click on the image to enlarge.

Yes, that is a can originally meant to hold gasoline (or petrol, for non-American readers), made by Shell, the well known oil company. These cans were issued to British troops as standard equipment with Vickers machine guns, to be used as steam chests!

In more advanced models, the steam chest was equipped with a manual pump, which allowed the users to pump the water back into the water jacket without moving the steam chest.

A Colt MG 38 machine gun. Click on the image to enlarge.

In the above image, we see a Colt MG 38 machine gun with its steam chest positioned at the left of the image. Note that there are two pipes coming out of the water jacket into the steam chest. The pipe on the right of the picture transports the steam out of the water jacket into the steam chest and the other pipe sends water back from the chest into the water jacket. Also note that the steam chest has a handle to the left of it. The user turns this handle, which operates the manual pump inside the steam chest and sends water back into the water jacket. With this design, the user does not need to lift the can to pour the water back.

It must be noted that steam chest systems aren't air-tight, so a little steam does always escape out. However, they allow their crews to re-use their water for a lot longer.

Steam chests were supplied with most heavy machine gun models made in between World Wars I and II. As water-cooled heavy machine guns began to be phased out of military inventories and replaced with air-cooled models, the need for steam chests went away as well. With the invention of improved metallurgical techniques for making barrels last longer at higher temperatures, as well as the development of quick-change barrels, the extra weight of the water jacket, water and the steam chest were simply not worth the trouble for most users. That is why no modern machine guns use steam chests any more.

Heavy Machine Guns - III: Modern HMGs

In our last couple of posts about heavy machine guns, we saw that they were weapons designed to fire rifle cartridges for long periods of time. Since they were designed for firing in automatic mode for hours, the designs were bulky and the early machine guns were water-cooled, which contributed even more to the weight. Therefore, these weapons needed multiple people to operate effectively and inconvenient to move around and were mainly used as defensive weapons. Heavy machine guns of this type were used extensively in the trench warfare conditions of World War I, against enemy infantry.

World War I also saw the introduction of armored vehicles, such as the British Mark-I tank and the German Junkers J.I airplane. Against such armor, ordinary infantry rifle ammunition (like the .30-06) was useless. Therefore, there was a need for a weapon that could defeat lightly armored vehicles, buildings, aircraft etc. and could do so at longer ranges. In 1917, General Pershing posted a request back to the US Army Ordnance Department, asking for a rifle to be designed, that could fire a bullet of at least .50 inches (12.7 mm.) diameter at a velocity greater than 2700 feet/second (820 meters/second). The famed designer, John Browning, went to work on this request. He took his earlier .30 caliber machine gun model and scaled it up to fire a .50 BMG (12.7x99 mm.) caliber cartridge. His initial design used water cooling, just like other heavy machine guns of that era. The design came too late to be used in World War I, but was accepted later by the US Army and Navy as the M1921 (curiously though, despite the name, it actually went into production in 1929!).

After Mr. Browning passed away in 1926, further development work on this gun went on, led by Dr. S.H. Green. By studying the needs of the US Army, Navy and Air Force, Dr. Green realized that a single machine gun model could not accommodate everyone's requirements. Hence, he redesigned the M1921 to a model that could be changed into seven different .50 caliber machine guns, all using a common receiver component, but switching the other components such as the barrel, water jacket etc. The new model machine gun was called the M2 heavy machine gun and was manufactured in its different versions by Colt, starting in 1933. One of the versions did not have a water jacket, but instead had a heavier air cooled barrel, which was designed to be quickly changed. The lack of the water jacket meant that the barrel had to have a larger surface area and have more mass to compensate, therefore this variant was called the M2 HB (HB standing for "Heavy Barrel"). However, this version was lighter compared to the water-cooled versions: the water-cooled M2 versions weigh about 121 lbs (55 kg.) and the air-cooled M2 HB only weighs 84 lbs (38 kg.) in comparison. Another even lighter version, with a thinner barrel designed exclusively for aircraft use, only weighs 60 lbs (27 kg.) and was used by many US aircraft in World War II.

It must be noted that World War II changed the nature of warfare in several ways. The German Blitzkrieg strategies showed the effectiveness of maneuver warfare and static machine gun positions that were so effective until World War I, became obsolete and useless. In this environment, a lighter heavy machine gun model that can be moved around relatively easily, is much more useful than a heavier water cooled model.

M2 Heavy Machine Gun on a M3 tripod. Public domain image.

While the M2 HB weighs 84 lbs. (38 kg.), it must be noted that the M3 tripod stand that it is mounted on weighs an additional 44 lbs. (20 kg.). The gun is also designed to be mounted on jeeps, armored vehicles, ships or anti-aircraft turrets. It can fire a variety of rounds, ranging from standard ball ammunition to armor piercing, incendiary etc. This weapon was very successfully used by various branches of the US military in World War II and continues to be used by the US military to this day. It is also used by military forces of many other countries in the world. It exemplifies the modern definition of the heavy machine gun, as we know it today.

To summarize, the early heavy machine guns were designed to use standard rifle ammunition, were water cooled and bulky, capable of long range firing, and designed to be used in static defensive roles. The modern definition of a heavy machine gun is a weapon that is designed to use much larger ammunition calibers, is air-cooled, has quick change barrels to solve overheating issues, is less bulky than water-cooled models, capable of long range firing, is designed to be moved around relatively easily, and can be used in both defensive and offensive roles. Modern heavy machine guns are designed to be used, not only by infantry, but also by jeeps, tanks, humvees, boats, ships, aircraft etc.

A M2 HMG in a firebase overlooking the Korengal valley in Afghanistan. Click on the image to enlarge. Public domain image.

US Marine from the 24th Marine Expeditionary Unit with a vehicle mounted M2 heavy machine gun. 

Click on the image to enlarge. Public domain image.

Modern heavy machine guns include the above mentioned M2, the Soviet DShK 1938 (another World War II era design), the Russian Kord HMG etc.

Heavy Machine Guns - II

In our last post, we looked at the early developments in heavy machine guns and the work done by Hiram Maxim. We will continue our studies on this topic today.

When we last left off, Hiram Maxim had invented the Maxim gun and had founded a company in England to manufacture them. What was not mentioned in the previous post was that he took on a partner for funding the new Maxim Gun Company. This partner was Albert Vickers, son of Edward Vickers, who was one of the founders of a prosperous steel foundry business and also had interests in manufacturing armor plating and shipbuilding. In 1896, the parent Vickers company bought out the Maxim Gun Company and got into the machine gun manufacturing business as well. Vickers took the basic Maxim gun design and simplified the firing mechanism and also used more modern alloys in the construction, thereby reducing its weight slightly. The Vickers machine gun was formally adopted by the British army in 1912 and was used pretty heavily in World War I, both by the army and the airforce (it was fitted into several British and French fighter aircraft).

Vickers machine gun in action during World War I. Click on the image to enlarge. Public domain image.

Like its predecessor, the Maxim machine gun, the Vickers also has a barrel surrounded by a water jacket, in order to cool down the barrel. Upon firing the barrel rapidly, the water would turn into steam and exit out via a port at the muzzle end, into a separate steam chest. Here, it would condense back into water. This system has the advantage that the rising steam does not give away the gunner's position and the water can be reused. It was recorded that if the water ran out, crews were known to pee into the water jacket.

In British use with the .303 cartridge, this weapon has a range of over 4000 meters. The gun weighs about 30 lbs (13.6 kg.) by itself, without any ammunition or water. With a full load of water (about 4 liters) in the water jacket, it weighs about 40 lbs (18 kg.). Then, there is the tripod stand, which weighs about 50 pounds (23 kg.) and the ammunition boxes, which contain 250 cartridges held in a cloth ammunition belt and weigh about 22 lbs (10 kg.) each. In addition to this, the weapon also comes with spare barrels, steam chest, pipes etc. With all this weight, the gun needed about six to eight people in a crew to operate it: one to fire the gun, another to assist with feeding the ammunition and reloading it and the rest to carry the weapon, extra ammunition and spare barrels. If the gun needed to be moved, the crew would disassemble it into lighter component parts, while one of them stood guard with an ordinary rifle.

The gun was designed to fire 10,000 rounds per hour, after which the barrel would have to be replaced by a new one. With a trained crew, this barrel replacement operation only took a couple of minutes to accomplish. Therefore, the gun could be used to fire almost continuously for very long periods of time. In August 1916, the British Army's 100th Company of the Machine Gun Corps fired their ten Vickers guns continuously in battle for about 12 hours straight. During this time. they interchanged about 100 barrels and it is recorded that they fired over 1 million cartridges without a single failure!

It was during World War I that the classification between heavy machine guns and light machine guns started. Light machine guns like the Lewis gun were issued to normal infantry units. Heavy machine guns like the Vickers were issued to new units called Machine Gun Corps.

As the reader can probably see, the differences between the light and heavy machine gun classifications now become clear. Light machine guns are lighter, come with bipods and are designed to fire short bursts of ammunition, whereas heavy machine guns are much heavier, are mounted on tripods or vehicles and can fire on automatic for much longer periods. Light machine guns are issued to advancing infantry units to support an attack, whereas heavy machine guns are more geared towards staying at a fixed position and defending against advancing infantry or cavalry.

The Vickers gun was known for reliability and was sold to several countries in a variety of calibers. It was in service with various countries from about 1912 to 1968. Unlike the light machine guns that we studied before, this gun is capable of firing almost continuously, literally for hours.

In our next post, we will look at the modern definition of heavy machine guns.

Heavy Machine Guns - I

In our last post, we looked at light machine guns. In today's post, we will look at another class of machine guns, the Heavy Machine Gun (often abbreviated as HMG).

In the late 1800s, there arose a need for a firearm that could fire in automatic mode, with good accuracy over longer ranges, for a long amount of time. Such a weapon could be used by a small group of soldiers in a key position to defend against a much larger group of enemies armed with inferior weapons and prevent them from advancing. Unlike light machine guns, these weapons needed to fire in automatic mode for much longer periods. This led to the development of heavy machine guns, weapons that can literally lay down huge volumes of fire, for very long periods of time.

The first heavy machine gun in history was the Maxim gun, invented in 1884 by Sir Hiram Maxim, an American inventor settled in England (he later became a British citizen in 1900). He was a prolific inventor and invented several items including a curling iron, several gas and steam engines, electric light bulbs, automatic sprinklers, motor cars etc. In 1882, he was in Vienna and ran into another fellow American that he knew from his time living in America, who informed him that "Hang your chemistry and electricity! If you want to make a pile of money, invent something that will enable these Europeans to cut each others' throats with greater facility." As a child, Sir Maxim had fired a large gun and had been knocked down by the recoil. This incident inspired him to invent a recoil operated machine gun (he also patented gas operated and blowback systems between 1883 and 1885). While he was inventing his gun, he announced in the local papers that he was experimenting with a new type of gun in his garden and advised his neighbors to keep their windows closed, in order to avoid getting injured by broken glass!

Maxim's first prototype weighed around 26 pounds (11.8 kg.), but was not capable of firing for long periods of time because of overheating problems. To solve this issue, he put a water jacket around his barrel. He also increased the caliber to fit a .303 British rifle cartridge. This made his rifle design heavier and it weighed around 60 pounds (27.2 kg.)

A Maxim machine gun. Click on the image to enlarge.

Image licensed under the Creative Commons Attribution-Share Alike 3.0 License by Jonathan Cardy at Wikipedia

Such a heavy gun required a team of people to operate: one man to fire the weapon and the others to reload ammunition, refill water, spot targets, help carry the gun and ammunition from one position to another etc. While Maxim tried to sell his invention to various European countries, many of them were suspicious about machine guns in general, because of jamming issues on previous models. Luckily for Maxim, the British had appointed Sir Garnet Wolseley as commander-in-chief in 1888 and he was a big believer in new technologies and placed an order for 120 Maxim machine guns in October, using the same .577/450 cartridges of the Martini-Henry rifle. The Maxim guns proved their worth in 1893/1894, in the First Matabele War in Africa., where a small unit of British soldiers armed with just four Maxim guns held off a force of 3500-5000 African Ndebele warriors. After this and several other encounters, other governments started to take notice and placed orders for heavy machine guns as well.

Early Maxim guns had a problem of heavy smoke obstructing the view of the gunner very quickly, but the invention of smokeless powders solved this issue. Incidentally, Hiram Maxim himself was one of the pioneers of smokeless powders and he and his brother, Hudson Maxim, were granted a patent for a particular type of smokeless powder. However, the patent was issued in the name of "H. Maxim" and his brother took advantage of this to stake a claim for the patent and later moved back to the United States, where he developed several more explosives and sold the rights to the DuPont Chemical Company. Because of this patent dispute, Hiram Maxim stayed in Europe, while his brother moved back to the United States and the brothers never spoke to each other ever again.

Due to years of experimenting with loud guns, Sir Hiram Maxim's hearing was damaged and he began to go deaf later in life. In a twist of fate, a device that could have saved his hearing, the Maxim silencer (suppressor), was invented by his son, Hiram Percy Maxim in 1908.

In our next post, we will look into further developments of heavy machine guns.

Machine Guns - General

In our last few posts, we studied different feed systems such as ammunition belts, chain feeds and feed strips. All these mechanisms are generally used with machine guns. Therefore, in the next series of posts, we will study all about machine guns.

A machine gun is a firearm that is capable of fully automatic fire. What this means is that as long as the firearm has ammunition available to it and the trigger is pulled, it will continue to load and fire ammunition automatically. Machine guns are capable of firing at high rates of several hundred rounds per minute and are designed to keep firing for considerable periods of time. The capability of maintaining sustained fire for long periods of time is what distinguishes a machine gun from an automatic rifle or an assault rifle (both of which can fire on full-auto only for limited periods of time).

US military doctrine has another interesting way of classifying automatic rifles versus machine guns. If the fully automatic firearm is operated by a crew, then it is a machine gun, but if a fully automatic firearm is operated by a single person, then it is an automatic rifle. In many cases, weapons fall exclusively into one of these two designations, however, we have one major oddball that falls into both categories -- the M249. US Army Field Manual FM 3-22.68 ("Crew-Served Machine Guns") describes the M249 as both an automatic rifle and a machine gun! Quoting from the manual chapter 4, section 5, paragraph 4-207, "Both the M249 automatic rifle and the M249 machine gun are identical, but its employment is different. The M249 automatic rifle is operated by an automatic rifleman, but its ammunition may be carried by other Soldiers within the squad or unit. The M249 machine gun is a crew-served weapon."

Machine guns can be portable as well as mounted and therefore, they are generally classified based upon size.

Before we dig deep into the topic, let us talk about submachine guns, which are portable firearms that are designed to fire pistol-sized ammunition. While they have a high rate of fire, some authorities do not consider these as "true machine guns" as they are not capable of sustained fire for long periods of time. Examples of these would be the Thompson submachine gun (which actually coined the term "submachine gun") also known as the Tommy gun, Chicago typewriter, Trench broom etc., Heckler & Koch MP5, Uzi etc. All these weapons are designed to fire pistol sized ammunition such as .45 ACP, 9 mm Parabellum etc.

Next, we have true machine guns like the Light machine gun, Medium machine gun, Heavy machine gun, General purpose machine gun which all use larger ammunition calibers (rifle calibers or larger). These weapons are generally heavier than other automatic weapons (even the "light" machine gun is heavier than an assault rifle, for instance). Examples of these would be the Lewis gun, the Bren gun, MG-34, Browning M1917, Browning M2, M60 etc.

A Lewis gun. Click on the image to enlarge. Public domain image. 

A M60 machine gun. Click on the image to enlarge. Public domain image.

We will study more into these various types of machine guns in the following posts.

Finally, we have weapons in the autocannon category. The difference between an autocannon and a machine gun has largely to do with the type and size of ammunition. If the firearm uses ammunition greater than 16 mm. diameter, or if it uses large caliber explosive rounds, then it is considered an autocannon rather than a machine gun. Examples of an autocannons include the M242 Bushmaster (which we studied briefly, when recently studying about chain guns), Oerlikon 20 mm. autocannon etc.

Since machine guns are designed to fire on automatic for longer periods of time, they tend to overheat quickly. Hence, many of them are either designed to have a built in barrel cooling system or feature a quick-change barrel replacement system. For the same reason, most machine guns are also designed to fire from an open-bolt, so that the breech area can be more efficiently air-cooled when the gun is not firing.

In the next few posts, we will study all about various types of machine guns and their history.