Pneumatic Guns

Gallery opened: 21 Oct 2015

Updated: 5 Dec 2022

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Pneumatic guns as such are not rare or unusual. They are very common in the forms of air rifles and air pistols. However, air-powered guns of larger calibre are indeed rare. The early versions such as the Zalinski dynamite gun were motivated by the instability of the shell payload to shock; driving it out of the barrel by an explosion gave a very good chance of it exploding in the gun barrel. This is known in the trade as a 'bore premature' and there is nothing that artillery men fear more. The use of compressed air to expel the shell meant that it could be accelerated relatively gently as it passed up the barrel. Developments in explosives removed this problem and pneumatic guns were at a big disadvantage because of their lack of range, and were abandoned apart from a few niche applications.

Lack of range is inherent in air-powered guns. The highest firing pressure in a pneumatic gun that I am currently aware of is the 2500 psi used by the largest Zalinski dynamite guns. In contrast, a common .22 cartridge can generate 16,000 psi and the US .30-06 rifle cartridge regularily reached 50,000 psi in the breech, with higher pressures reached in proof tests. Modern lubricated reciprocating compressors achieve 4500 psi, and non-lubricated reciprocating compressors 1500 psi. (The distinction is vitally important in the chemical processes where oil contamination must be avoided, but is unlikely to be a problem with pneumatic guns) These compressors are very large, heavy, and expensive and require enormous amounts of power, as compressing air is a very inefficient business. A great deal of heat is liberated as the air is compressed, and unless there is some way to use it locally all its energy is lost. Since the pneumatic gun compressors were sited away from the guns the heat would inevitably be lost and the whole process was highly inefficient.

They did not however disappear for good; it was noted by Theodore Roosevelt, during the Spanish–American War, that the Sims-Dudley dynamite gun was relatively quiet and did not emit smoke, and so did not draw counter-battery fire. Several of the combatants in WW I made use of pneumatic mortars to fire shells a short distance with a high trajectory, the Austrians being particularly keen on the idea, but there were no pneumatic guns as such.

This page deals only with guns and mortars powered by air. There have also been guns designed that were powered by gas, (usually CO2) by steam, and in one baroque example powered, at least in part, by exploding a mixture of ether vapour and air, using the Diesel effect. These others deserve pages to themselves.

THE TECH OF PNEUMATIC GUNS

1) There must be a sufficient local reservoir of air so the pressure behind the projectile builds up quickly, and a fast-acting valve to apply it. If it does not the projectile will just slide slowly out of the end of the barrel, flopping nose-first onto the ground. If it is fitted with an impact fuse, things will not end well. Some pneumatic ordnance used some kind of detent. (eg a screw that sheared when launch pressure was reached)

2) The compressed air must be cut off in a timely fashion, preferably just as the projectile leaves the barrel. The high-pressure air is a precious commodity, created by the expenditure of a lot of fuel, and it must not be wasted.

THE MEFFORD DYNAMITE GUN

Left: The Mefford dynamite gun: 1883

In 1883 a Mr David Mefford from Toledo, Ohio built a pneumatic gun that was delivered to Fort Hamilton in New York harbour. A Lieutenant Zalinski was assigned to test this gun. It consisted of a brass tube 28 feet long with an internal diameter of two inches, and a wall thickness of approx 1/4 inch- much less than the barrel of a conventional gun, and so much lighter. The associated reservoir held 12 cubic feet of air at 500 psi, and was connected to the breech by a simple rubber hose. Firing was by manipulating a straightforward cock valve.

Picture from Mefford's US patent 279,965 of 1883. The patent describes how the shock of launching could be reduced by leaving an air-space between the breech and the base of the projectile. It also states that the gun has "no sensible recoil" though it must have had some.

The picture shows a supporting girder undeneath the barrel, which being much lighter in construction than a conventional barrel, would otherwise droop. This was also a feature of the Zalinski dynamite gun.

Mefford was granted an earlier US Patent No. 252,488 in 1882, but this describes a recoil system for a conventional gun.

The picture shows a simple one-stage compressor driven by steam. This would be a very inefficient way to compress air to 500 psi- a two-stage compressor with intercooling would be much better.

The Mefford dynamite gun has no Wikipedia page.

THE GRAYDON DYNAMITE GUN: 1889

The Museum Staff have recently uncovered reports of another pneumatic dynamite gun, put forward by a Lieutenant Graydon. The only information that has emerged so far is two newspaper reports. This is rather curious because if the reports are to be believed the Graydon gun was a large-scale operation, involving a gun that weighed 11 tons just for the barrel. There is plenty of information to be found about the Zalinski gun, why not the Graydon?

Left: The Graydon gun: 1891

This engraving, presumably derived from a photograph, was published in the USA journal Iron Age in March 1891

The photograph above shows a large U-shaped pipe that apparently introduces the compressed air through one of the trunnions; the bulging part may be the control valve. To the left of this are what appear to be eight vertical air reservoirs. The total reservoir capacity looks small compared with that used by Zalinski and it is not clear how the compressor was connected.

This news item below appeared in The Queenslander on Sat 14 Dec 1889, p1131:

THE ZALINSKI AND GRAYDON GUNS: WAR OFFICE EXPERIMENTS.

"In order to give the War Office an opportunity of judging of the comparative merits of the Graydon and Zalinski systems, a trial (the Birmingham Post Bays) will take place some time next year at Portsmouth; not, as in America, with dummy shells, but with charged ones. With a view to this trial, the syndicate formed for working the Graydon patents (numbering now thirty-eight) have contracted with Taunton, Delmard, Lane, and Co, Limited, of Birmingham, for the manufacture of a 15-inch torpedo-projector. This will be 30ft. long, as compared with a length of 55ft, which is necessary for throwing the same sized projectile containing 600 lb. of dynamite from a Zalinski gun. And whereas the range of the Zalinski is a little over a mile, the Graydon projector will land its torpedo in a fort or on a ship three miles distant. These two advantages— greater wieldiness in tbe weapon and greater range— are in part due to the fact that Lieutenant Graydon employs a pressure of 5000 lb to the square inch, while Zalinski only uses a pressure of 2000 lb. A bill has been introduced in the United States Congress for the purchase of a large number of pneumatic guns to fulfil certain conditions, which at present are only fulfilled by Lieutenant Graydon's projector. Though the guns would be made in America, it is likely, in the probable event of the Graydon gun being selected, that the orders for tbe compressors would for some time be placed with the Birmingham firm."

Note that Zalinski is mentioned, and so must have been active in 1889.

The above report was published, with some variations, by newspapers all over the world. This version below from The Practical Engineer for 1st November 1889 gives some more details at the end. The text duplicated above is grayed out:

THE MANUFACTURE OF DYNAMITE GUNS IN BIRMINGHAM.

"In order to give the War Office an opportunity of judging of the comparative merits of the Graydon and Zalinski systems of torpedo warfare, a trial will take place sometime next year at Portsmouth, not — as in America— with dummy shells, but with charged ones. With a view to this trial, the syndicate formed for working the Graydon patents — numbering now 38 — have contracted with Taunton, Delmard, Lane, and Company Limited, of Birmingham, for the manufacture of a 15in. torpedo projector. This will be 30ft long, as compared with a length of 55ft, which is necessary for throwing the same sized projectile containing 6001b. of dynamite from a Zalinski gun. And whereas the range of the Zalinski is a little over a mile, the Graydon projector will land its torpedo in a fort or on a ship three miles distant. Messrs. Taunton, Delmard, Lane, and Co. have obtained the contract on account of their unique success in making tubes to resist these heavy pressures, compressed air work being one of their specialties. At present only the 15in. gun has actually been ordered, but negotiations are proceeding, as the result of which it is hoped the order will come to Birmingham for a 6in. siege gun, throwing a torpedo charged with 70 lb of dynamite. The whole of the equipment of the guns, including carriages, compressors, and boilers, will be made by the same contractors. The larger gun, with its complete outfit, costs about £10,000, and though the full complement of compressors will not be furnished with the experimental weapon, the present order is obviously an important one as affecting local trade. The first gun will take till Christmas to complete."

And then this appeared a year later in the Daily Alta California, Volume 83, Number 182, 29 December 1890:

LARGEST DYNAMITE GUN.

It Has Just Been Finished and is to use Compressed Air. (Pall Mall Budget)

"Messrs. Taunton, Delmard, Lane & Co. of Birmingham are just finishing tbe largest dynamite gun which has yet been made. The explosive contents are made up for greater safety in tiny waxen pellets, and lodged in a shell, the true flight of which is secured by a tapering telescopic tail; and the gun is to be discharged by the expansion of condensed air at a pressure of 5000 pounds per square inch, tbe impulse of which is a safer propelling energy than the ignition of any kind of powder, because it does not operate so suddenly as to cause a danger of the premature explosion of the missile. The telescopic tail enables Lieutenant Graydon to shorten his shell by one half, and to reduce proportionately the length of the impulse tube or gun proper, while the uso of a pneumatic charge makes it possible, without danger, to construct the shell more flimsily than would otherwise be the case."

"The contract -with Messrs. Taunton & Co. is for a 15-inch torpedo projector which will throw a charge of 500 pounds of dynamite a distance of three miles; it is expected that this contract will be followed by orders for still larger weapons. As soon as the gun now in hand is delivered there will be a trial of its powers at Portsmouth against the Zalinaki gun, not with dummy shells, as in the case of the American experiments, but with actual charges of dynamite. The noise of the discharge being small, the projectile might be dropped into a fort or onto a ship without giving the besieged any intimation of the quarter from which the attack came. The concussion when the dynamite exploded would in all probability be violent enough to put a large garrison hors de combat, even if they were not wounded by debris; and, truly aimed, a single shell would destroy an ironclad. The barrel, or pneumatic tube, of the gun is of Whitworth forged steel, and weighs about eleven tons."

A longer version of the above report appeared in The Daily Telegraph in 14 Feb 1891. The first part was just as above, but the following mass of detail came after it:

"It (the barrel) is supported at the breech end on fixed trunnions 15in in diameter, which are hollowed for the passage of the compressed air. Towards the muzzle it is carried on movable trunnions engaged with two forged steel arms or levers. These clevers have sliding fulcrums, and are actuated by a hydraulic plunger for the purpose of elevating or depressing the gun. The breech is closed by means of a steel screw-block with interrupted threads, as in heavy service ordnance."

"A peculiar feature of this particular Graydon gun is that it can be loaded at any degree of elevation in its working range. Pivoted to the breech trunnions there is a loading slide or tray fore the reception of the projectile or torpedo, the weight of which is about one ton. This slide, at all times when the barrel is elevated above the horizontal line, rises by hydraulic pressure to receive the projectile from a tram trolley. By opening a valve the slide is then made to descend with its load, and becomes lineable with the barrel of the gun. On each side of the barrel is fixed a small double-acting hydraulic cylinder, the plungers of which not only control the movements of the loading slide, but also, by their continued action, draw the projectle up into the barrel, where it is held. The breech-closing block, suspended above the trunnions by counterweights, then descends, and is also drawn into the breech by the crosshead of the hydraulic plungers, and locked. The gun is now ready for discharge."

"The compressed air reservoirs, a complement of which numbers thirty-two, are 4ft long and 10in in diameter, are metal of metal 3/4in thick, and are the invention of Mr Lane. They are tested to a pressure of 4 tons to the square inch. They are carried with the gun in four sections of eight each, two on each side of the gun carriage. Filled with air compressed to 5000 lb per square inch, or about 1/340 of its original volume, the capacity of each at the working pressure is 17,000 cubic feet of air, weighing 11cwt in its compressed condition. Any number of the four sections may be discharged, according to the range desired or the weight of the projectile. The discharging valves are a peculiar arrangement of the piston type, and are packed on the hydraulic system. All valves and pipes, were not forged, are of Whitworth cast steel.The carriage on which the gun is mounted is constructed of heavy steel plates, with massive trunnion bearings of cast iron, secured to it buy means of numerous turned bolts. The carriage i ssupported on the roller path with conical rollers geared together and actuated by a Hennan & Froude spherical engine, the motive power of which is also compressed air. The roller path, which will ultimately be bedded in concrete, is made of sections of cast iron. It is 21ft in diameter, and is planed on its surface."

"The air from the compressors is passed to the reservoirs on the gun-carriage through a central pivot or swivel-tube. The gun can be loaded, elevated, trained, and discharged by one person. With the gun there is of course a special air compressor. this is a modification of the high-pressure machines designed by Mr H Lane (now largely in use in this country, and adopted by several foreign governments) for oxygen, hydrogen, and carbonic acid. The air is compressed in four operations, the piston decreasing in diameter at each stage. The first, which draws the air from the atmosphere, is 12in in diameter, and the last, which delivers it to the reservoirs, is 2-1/4 in. After each operation the air is cooled by a tubular coil, surrounded with water."

"The designing and the construction of the pneumatic gun has been carried out by M Lane, engineer to the company, under the supervision of the inventor, Lieutenant J W Graydon, of the United States Navy who has been residing in Birmingham with that object. It is in some measure due to him that the apparatus for throwing highly-explosive shells considerable distance with accuracy is at present engaging the serious attention of all the Powers. a pneumatic gun is now being erected at Shoeburyness for trial by the British Government, and the United States Government has not only spent already a great deal of money on this class of weapon, but has set aside funds for the purchase of 25 of them. Five European governments have sent representatives to Birmingham to see and report upon the Graydon project during its construction; and the Chinese and Japanese and South African governments profess themselves greatly interested in its success."

The reference to a Heenan & Froude spherical engine caught my eye. This is none other than the remarkable spherical engine of Beauchamp Tower. Heenan & Froude were the manufacturers.

This all seems very mysterious. The Zalinski gun is quite well documented, and many photographs and drawing of its various versions are available. But there is no trace of any image for the Graydon gun, although it must have been a substantial piece of machinery with its 15-inch 11 ton barrel. The Museum Staff are suspicious by nature, and wondered if this might be an imaginary gun thought up for stock-market fraud. On the other hand Messrs. Taunton, Delmard, Lane & Co. of Birmingham were a genuine and well-respected firm with great expertise in high pressures, and it seems very unlikely they would have involved themselves in criminal stock-promotion. Four-stage compression with intercooling is described, and seems an eminently practical way of reaching the required pressures.

Advertisements for the Howard Lane and the Taunton, Delmard, Lane companies. They are clearly well up in the high-pressure business.

Taunton, Delmard, Lane state they are ready to handle pressures up to 3 tons per square inch; this is 7500 lb per square inch, so Lieutenant Graydon's 5000 lb per square inch should not have caused too many qualms.

The ad on the left carries an intriguing reference to 'compressed gas motors'.

Left: This appeared in a San Jose newspaper on 29 October 1900

This makes it appear that Mr Graydon did not do well from his inventions. But... according to The National Cyclopedia of American Biography for 1906, he was not only still alive but actively engaged in developing "military and naval devices".

I am developing a dark suspicion that the letter to the Star might have been sent maliciously by someone else.

There were at least two more little-known dynamite guns; one by Maxim. The other was by Dr Joel Gilbert Justin, which attempted to fire dynamite shells with conventional gunpowder; the dynamite was in the form of little balls embedded in wax, but this does not seem to have helped much. At a demonstration on 27 May 1890 a modified cannon exploded, putting the watching crowd in great peril, though no-one seems to have been seriously hurt.

Research continues...

THE ZALINSKI DYNAMITE GUN: 1894

Left: Early Zalinski dynamite gun: 1894

The Zalinski dynamite gun is the best known example of a pneumatic gun. In fact, as freely admitted by Zalinski himself, he was a developer of Mefford's idea rather than the inventor. This is one of his early experimental models. Note the supporting girder, which is much larger than the barrel. The compressed air for launching is supplied through the trunnion of the mounting yoke, a much more practical method than Mefford's rubber hose.

Inset top left is one of the projectiles, which carried 25 kg of blasting gelatine rather than dynamite as such. With this Zalinski was able to blow up the old wooden schooner 'Silliman' while foreign military advisers watched. I would have thought it might have been better to keep it secret.

This design looks a little strange. What are presumably handwheels to alter elevation and training are arranged so that all three have to turned in synchrony to point the gun. It appears to be a useless arrangement even for a prototype.

The Zalinski dynamite gun has a Wikipedia page.

Above: Early 8-inch Zalinski gun on trials: 189?

This looks noticeably different from the drawing above. The horizontal cylinders behind the man with the binoculars (Zalinski himself, perhaps?) are the air reservoirs, apparently connected to the breech at the right by the vertical pipe.

The puff of 'smoke' (actually condensed water vapour due to the rapid cooling of the expanded air) indicates that a projectile has just been launched.

Left: Early 8-inch Zalinski gun drawings: 1890

These drawings do not correspond very closely with the photograph just above. The drawings show two joints in the barrel instead of three, and four uprights in the support truss rather than six.

RAPIEFF COASTAL DEFENCE GUNS

Captain Rapieff was a former Russian artillery officer living in the US. He was the chief engineer of The Pneumatic Dynamite Gun Company of New York, formed to exploit pneumatic guns once Zalinski had proved their potential. Captain Rapieff does not have a Wikipedi page.

Left: Three 15" Rapieff dynamite guns: 1894

Three guns of 15-inch calibre, shown here, were installed at Battery Dynamite, Fort Winfield Scott, San Francisco. Two more were placed at Fort Hancock at Sandy Hook, New Jersey, and one each at Hilton Head, South Carolina, and Fishers Island, New York.

Left: Rapieff coast defence gun: 189?

The launch pressure was 1000 psi and the reservoir pressure 2000 psi. Note the hefty girder supporting the barrel. The associated boilers, steam engines and air-compressors weighed some 200 tons. There is more than a hint of Jules Verne about the whole business.

Left: Rapieff coast defence gun: 189?

Some details of the gun are shown here. The gun is still fed with air via a trunnion. The air mains are of large diameter, contracting at the joints, presumably to reduce the stress on the joint flanges. In this way the pipes themselves had significant storage capacity, presumably so there was a reservoir of air immediately adjacent to the gun so launch pressure could be built up quickly.

A projectile is shown on a trolley ready for loading.

Left: Rapieff coast defence gun: 1894

Here the gun is being loaded with a 500-pound projectile from a trolley running on rails around the gun. A projectile is shown on a trolley ready for loading. It looks as if loading could only be done at one elevation.

The air release mechanism is presumably the equipment on top of the breech, with a handwheel at the far end. The gun was apparently fired from the small platform by the left trunnion. Note the big brass gauge here, no doubt to measure the available air pressure. This view indicates that loading was done through a hinged breech door as in conventional guns.

From The American Engineeer, September 1894, p396

Left: Rapieff coast defence gun: 1894

Another view of the loading procedure. Here the breech is closed.

DYNAMITE GUNS AT SEA

The 239-ton steamer USS Vesuvius was built 1887-88 and commissioned in June 1890. She was fitted with three 15-inch Zalinski guns firing at a pressure of 1000 psi.

Left: USS Vesuvius: 1890

The great snag was that the guns were fixed to the hull in both elevation and training; the effective elevation could be altered by changing the firing pressure, but the guns could only be aimed by pointing the whole ship. This made for poor accuracy, and while in her Spanish-American war service her projectiles dug impressive holes in the countryside their impact was mostly psychological. In 1904 she was converted to a torpedo testing ship, in which role she was almost sunk by one of her own torpedoes circling back and hitting her, and finally decommissioned in 1922.

At upper left can be seen a row of pipes (looking rather like a string of a sausages) which are of the same unusual shape as in the Rapieff illustration above, presumably with the same intention of providing storage volume without excess strain on the joint flanges.

A projectile is shown at the bottom of the picture.

Left: The Vesuvius plan and section: 1890

The 15-inch gun barrels can be seen slanting upwards on the right side of the bottom diagram. While this drawing is not too clear, it looks as though the air compressors are the dark shapes just aft of the engines. This would have avoided running shafting through the central boiler-room. The long cylinders on the right of the second drawing down are probably the air reservoirs.

This diagram gives a good clue as to why the guns were fixed. The barrels needed to be long so that enough velocity could be given to the projectiles from a pressure that was low compared with explosives. Since they are something like a quarter of the length of a relatively small ship, it was not practicable to put them on a rotating mounting.

Left: The Vesuvius 'dynamite gunboat': 1890

Three ominous-looking muzzles can be seen protruding through the foredeck.

During the Naval Revolt of 1893-1894, Brazil called on Captain Zalinsky to install a single 15 inch pneumatic gun aboard the converted Brazilian Nictheroy (ex-El Cid) in 1893. This weapon was installed in an electrically powered open mounting that could be elevated, and trained through an arc of 300 degrees; a considerable improvement on the fixed guns of the Vesuvius. The crew for this weapon was one officer and 14 men. The Brazilian navy was at the time in a dire state, and their only option was to hire mercenaries. Flint, the American 'admiral' of an small and assorted fleet, recalled: "The only odd feature was that there was not a man aboard the ship who who had ever seen the (Brazilian) flag before, or who could speak the language of the country for which he was faring forth so gallantly to fight." Flint made no pretence of caring about Brazilian politics; this was just business.

Left: Rapieff pneumatic gun installation on the Brazilian cruiser Nictheroy: 1894

The gun looks very much like the 15-inch weapons used for US coastal defence. There is the characteristic handwheel on top of the barrel, and the brass pressure gauge by the left trunnion. Two rectangular shield plates have been added to protect some of the gun crew, and there is now a big cylindrical structure of unknown function over the breech.

Zalinski was unwell and unable to sign on for the voyage from the US (where the mercenary fleet was assembled) to Brazil, but he was on Nictheroy for her initial gunnery trials, supposedly being paid a hefty £15,000 for a month's service.

Quoting from a "Proceedings of the United States Naval Institute, 20, #72" article:

"A correspondent on board that vessel writing under date of March 15, 1894 says Captain Baker and the other officers speak in enthusiastic terms of the trial of the cruiser's famous dynamite gun; just before entering the harbor on the day of the surrender of the rebel forces, a shell was fired at Pai Island in the bay and all agree that the explosion was 'fine'." It was probably fortunate that the mutineers surrendered, as the pneumatic gun was apparently disabled by this first shot. The gun's commander was suspected of being a traitor and was disrated as a result. (Which sounds very strange- if he really was some sort of saboteur you would have though he'd be shot) The Nictheroy was disarmed and the pneumatic gun was then reportedly mounted as a coast defense weapon at Fort Sanata Cruz.

This account is rather puzzling because, as noted above, the crew of the Nictheroy were all US mercenaries, and not likely to be seduced by the rebel cause.

One of the first submarines, the USS Holland, built by John Holland with contributions from Zalinski, had a 8.4-in dynamite gun designed to fire "aerial torpedoes".

ZALINSKI GUNS IN ENGLAND: 1894?

I was much surprised to find a Zalinkski gun had been installed for trials in England. Here is an account by Penrose Fitzgerald, who took charge of Pembroke Dockyard on the 9th of February 1893, and spent two years there, being promoted to the rank of Rear-Admiral on the 20th of February 1895:

"Next year we had another Royal visitor. The Duke of Cambridge came down to inspect some troops, which were paraded for him in the dockyard. He expressed a wish to see the famous Zalinski gun fired. The Zalinski gun was a sort of gigantic pop-gun fired with compressed air. It was sunk into the ground in a trench, and, as well as I can remember, it could not be trained horizontally, though it admitted of some adjustment of elevation. It was more of a tube than a gun, and it hurled into the air (if it went off) a projectile which was more of an aerial torpedo than a shell, and the said projectile was fitted with a delayed-action fuze, which was intended to become operative a few seconds after the missile had struck the water. It was not necessary to hit an enemy's ship in order to destroy her, for if the missile exploded anywhere near her she would be blown to smithereens - at least, so said the inventor."

"The Zalinski gun was mounted at Dale, on the western shore of the entrance to Milford Haven, about nine miles from Pembroke Dock; and as the Duke had expressed a wish to see the gun fired, I took him and his staff down to Dale in the Dockyard tug Stormcock, and as we were to make a day of it, I provided them with lunch. I had been told that the Duke was fond of pork chops, so I made ample provision in that respect, and pork chops formed the principal item in my menu. My information was apparently correct, for the Duke polished off three or four pork chops and was in the best of humours, as also was the chief of the staff - the late Sir Redvers Buller, of South African renown."

"On our arrival at Dale, orders were given to fire the Zalinski gun and drop a projectile just outside the entrance; while the Stormcock, with the Duke and party on board, lay-to just inside to watch the effect; but after waiting along time and nothing happening, a signal came from the shore to say that the gun would not go off at present and there was no knowing when it would go off - if ever.
The Duke was very grumpy, used some quite uncomplimentary language about the Zalinski gun, and told me to take him home."

This is from the second volume of Penrose Fitzgerald's autobiography 'From Sail to Steam'. It appears that the year is 1893 or 1894.

More information on the Zalinksi gun in England surfaced in Coast Defences of Ebgland & Wales by Master-Gunner Ian Hogg. (David & Charles, 1974)According to Hogg, a 10-inch calibre Zalinski gun was given initial trials at Shoeburyness, then installed in Dale Fort at Milford Haven. Numerous trials were fired against a paddle-steamer borrowed from the Admiralty. The Ordnance Committee turned down the weapon as it disliked the complications of the air compression machinery, and because the performance was not as good as conventional guns. A good call.

It seems strange that the calibre reported is 10-inch, because the American guns appear to have all been 15-inch, apart from the 8-inch prototype.

THE DUDLEY DYNAMITE GUN: 1898

Left: The Dudley dynamite gun: 1898

This rather cumbersome looking weapon is the Dudley dynamite gun, the forerunner of the Sims-Dudley dynamite gun. A blank shell (ie powder only) was fired in the lower barrel A, providing hot gas that passed up the passage a and propelled the shell out of the upper barrel. The large volume of A meant that the pressures developed were much lower than in a conventional gun, where there is no air-space between the propelling charge and the shell.

This does not look a very practical design. There is a lot of heavy metal and it is necessary to work two breech mechanisms to load the shell and the propellant cartridge.

The item L at the end of the lower barrel A appears to be some sort of bursting disc to prevent the development of excessive pressure. Standing in front of that probably would not be a good idea, but then standing in front of the upper barrel with the shell in it would not be a good idea either.

THE SIMS-DUDLEY DYNAMITE GUN: 1898

Left: The Sims-Dudley dynamite gun: 1898

Presumably as a result of the involvement of Mr Sims, the design of the Dudley gun was much streamlined, with the gas-generating barrel now immediately beneath the projectile barrel, and mechanically supporting it. So far as one can tell at this scale there are still two separate breeches, but at least now they are close together. The junction between the two barrels now seems to be at the breech end for both.

The US government bought sixteen Sims-Dudley guns for the army, one of which was used in the siege of Santiago during the Spanish-American war.

Left: The Sims-Dudley dynamite gun: 1898

A propelling cartridge (the small vertical cylinder) and a projectile are visible in front of the gun.

Left: The Sims-Dudley dynamite gun: 1898

A Sims-Dudley in the field in the Spanish-American war. This website has a good deal of information on the use of the Sims-Dudley in action.

THE DORMOY-CHATEAU 50mm PNEUMATIC MORTAR

According to some sources this mortar was the 'ancestor' of the Brandt 60mm mortar shown below.

Left: Dormoy-Chateau 50mm pneumatic mortar

The Dormoy-Chateau mortar had a rather crude firing mechanism involving the rapid removal of an air-tight cap from the muzzle. The cap, with the remains of its sealing washer, can be seen hanging down from the muzzle; it seems to have been released by a rope lanyard, which would appear to be likely to disturb the aim. This rather suggests some hasty improvisation was done at the design stage. The maximum range was about 300 metres. The weapon appears to have been withdrawn before the end of the war as it does not appear in 1918 manuals.

Here some sort of horizontal reservoir appear to be fited at the bottom of the barrel. This is not shown in the drawing below.

The brass fitting on top of the barrel is almost certainly a pressure-gauge.

Displayed in the Musée Royal de l'Armée in Brussels.

Left: Dormoy-Chateau 50mm pneumatic mortar

This document shows the firing system. The compressed air reservoir was simply the bottom part of the barrel, the projectile being positioned by a metre-long long rod attached to its base. The lid over the muzzle was removed rapidly by a lever system and the air below the projectile launched it on its way.

Left: Dormoy-Chateau 50mm projectile

It all seems a bit bush-mechanic, as my friend Gareth would say. The projectile had to drag that long rod with it, which must have cut the range. Perhaps it had some stabilising function, as well as positioning the projectile in the barrel, but other mortars managed without so much dead-weight.

THE BRANDT 60mm PNEUMATIC MORTAR

The Brandt 60mm pneumatic mortar was invented by Edgar William Brandt, apparently in 1915. He has a Wikipedia page. In 1916, the French army placed an order for 3,000 of these mortars, plus 3 million shells, with Brandt's company. Brandt's father was a displaced person from Alsace after that province was grabbed by Germany in the Franco-Prussian war, which explains his germanic-sounding name.

Left: The Brandt 60mm pneumatic mortar: 1915

The Brandt mortar had the advantage that it weighed only 17 kg (without the bottle of compressed air, however) but the projectile was also light at 0.65 kg, (0.95kg from another source) and the maximum range was only 600 metres. It was fired at a fixed elevation of 42 degrees, but pressures ranging from 10 to 40 psi could be used to give a desired range less than this.

Here the air hose can be seen running into the underside of the mortar. Bill Todd has pointed out to me that the chap with the moustache is holding not a firing lanyard, which would have pulled such a light piece off target, but a Bowden cable, ie like a camera shutter release cable. This would transmit no net force to the mortar.

At least one source on t'Net asserts that the Brandt mortar was powered by compressed CO2. This is quite incorrect. CO2 would not be available in the field for recharging the cylinders, but air certainly was.

In a conventional gun, the larger diameter at the breech would indicate reinforcement to deal with the firing pressure. In this case it is actually a cylindrical air reservoir coaxial with the barrel. In a pneumatic gun it is essential to release a lot of air quickly behind the projectile, and letting it trickle to its destination through a narrow hose will not work. Here the reservoir was charged via the hose, but its entire contents were applied to the projectile almost instantly by the opening of a piston valve that gave free communication between the reservoir and barrel.

Left: Brandt 60mm mortar just after firing

This shows what may have been an unexpected snag with pneumatic mortars. As you can see here there is a puff of water vapour produced when the compressed air expands. (The same effect can be seen with the Zalinski gun above) It is probably much less than the smoke from a conventional mortar, but it does underline that these weapons were no more completely invisible than they were completely silent.

The discarded gas cylinder has presumably been emptied, and the two men immediately to the left of the muzzle are holding hand-pumps for recharging the reservoir; it is likely this was pretty hard work. Up to three pumps could be used simultaneously.

Left: Brandt 60mm mortar just after firing

There is a fine video on Youtube of a Brandt 60mm pneumatic mortar being fired. It is presumably a demonstration as one of the men is in civilian clothes, wearing a flat cap. This is just after firing; note the visible cloud of condensation at the muzzle. The man in the centre is holding one of the projectiles.

Thanks to hw97karbine for bringing this to my attention. He has a YouTube channel here.

Left: The firing mechanism of the Brandt 60mm mortar

Two apparently different diagrams of the firing mechanism exist, and this is taken from the clearer of the two. The piston is held in the sealing position by the over-centre action of the small lever with the leaf spring on top of it. The Bowden cable moves it over-centre in some way not yet clear, and the piston moves backwards very rapidly, appyling the compressed air to the projectile. According to the text accompanying the drawing, the mechanism then resets itself by means of two springs; in particular the big spiral one pushes the piston back into the sealing position when the air pressure is gone. Note that the thing like a revolver hammer moves backwards when then gun fires, and it looks as if it needs to be pushed in to re-cock the mechanism. Pulling the hammer back directly would fire the mortar, but you might lose your thumb. Perhaps only for emergency use if the Bowden cable breaks when the sale boche are attacking?

Another nice feature is that as soon as the piston moves backwards, air pressure also comes onto its centre, which presumably gives a nice positive-feedback snappy opening, just like the old pop safety valves on steam locomotives. I can remember the dreadful noise they made.

Superb animation kindly provided by Bill Todd

Left: Brandt 60mm mortar projectile

The usual projectile was a fragmentation type with a percussion fuse in the nose. (missing in this picture) Incendiary, message-carrying, or chemical types (with a glass body) were also used.

The Brandt 60mm pneumatic mortar does not appear to have a Wikipedia page.

Brandt's company is now known as TDA and still makes mortars.

THE BOILEAU-DEBLADIS 86mm PNEUMATIC MORTAR

Left: Boileau-Debladis 86mm pneumatic mortar

This is the Boileau-Debladis mortar allegedly in use, but it is probably a posed photograph, judging by the clean uniforms of the soldiers. The man on the right is holding one of the finned projectiles. The range has been quoted as an unimpressive 273 metres. The projectile weighed 1.53 kg, of which 0.45 kg was explosive.

Like the Brandt 60mm mortar, this has a closely-attached air reservoir, in this case the cylinder mounted under the barrel. Details are currently in short supply, but the item sticking out from the bottom of the barrel is almost certainly the valve that puts the reservoir in communication with the barrel.

From the New York Times 17 Feb 1918. The weapons was actually introduced in 1916, so this is not exactly hot news.

Left: The Boileau-Debladis 86mm pneumatic mortar

Displayed at the Invalides Army Museum in Paris.

In the left background, under the barrel of the Boileau-Debladis, is what is believed to be an Aasen gas-operated (NOT pneumatic) mortar.

The Aasen mortar was a 3.5-inch (88.9-mm) mortar, invented in France in 1915 by Nils Aasen, a Norwegian. The bolt action on top of the barrel fired a blank rifle round which produced gas pressure behind the projectile. It was adopted by Imperial Russia in 1915-1916, and was also used by the French, who called it the "Obusier Aasen de 86mm". According to "Les Canons de la Victoire 1914-1918" Vol.3 more than 2000 Aasen mortars were delivered to the French Army.

Left: The valve of the Boileau-Debladis 86mm pneumatic mortar

This sectional drawing (of less than stunning quality) unfortunately only gives a few clues as to how the valve operated. The small sketch at lower right shows a piston valve moving upwards to connect the reservoir to the barrel. The main drawing shows only the top of the valve where it mounts on the barrel. (marked corps du canon)

The valve is described as automatique which means that it operated when the stored air pressure rose enough to equal the setting made by the big knob at the top; this controlled the range.

Left: The Boileau-Debladis valve animated

Here is another brilliant animation by Bill Todd. You can see others in the rotary steam engine gallery.

Here is Bill's description of how the valve works. It is far more perceptive than mine.

"The valve is a balanced pressure design. The drawing shows it in the open position . Missing from the drawing is the lower part of the corps du canon with the sealing ring seat from the reservoir d'air.

"When the air pressure in the reservoir is low the outer piston is forced down against the seal ring by the large spring. As the air pressure increases, flowing through the restriction in the central piston shaft, the outer piston is held down against the seat by pressure above the diaphragm (barely visible in drawing). The valve opens when the reservoir pressure is enough to lift the central piston against the adjustable spring load.

"When the central piston has lifted enough for the top seal (leather presumably) to open to the ports, the pressure above the diaphragm drops rapidly and pressure from the reservoir d'air forces the outer piston up, opening the valve.

"High pressure air trapped between the restricted orifice in the bottom of the outer piston, and the central piston lower seal will keep the central piston up and the top valve open, until it escapes both to the barrel and up via the ports.

"When the central piston is able to move down (forced by the adjustable spring) and close the top ports , pressure will equalise on the diaphragm and the valve will close, ready for the next shot.

"The above probably happens fast enough to preserve a substantial amount of pressure in the reservoir d'air."

Many thanks to Bill for this description.

Left: The exterior of the Boileau-Debladis valve, modelled by Bill Todd

The black scale was calibrated for firing-pressure/range.

The Boileau-Debladis pneumatic mortar does not appear to have a Wikipedia page.

THE 120mm BRANDT-LHUILLIER PNEUMATIC MORTAR

Left: 120mm Brandt-Lhuillier mortar

The Brandt-Lhuillier is the mortar in the foreground. It appears to have a hinged breech that looks very similar to the The Austrian 12cm pneumatic mortar.

Information on this device has proved very hard to find. I would be grateful if anyone can help.

The 120mm Brandt-Lhuillier pneumatic mortar does not appear to have a Wikipedia page.

THE AUSTRIAN 8cm PNEUMATIC MORTAR

Left: Austrian 8cm pneumatic mortar: 1915

The 8 cm Luftminenwerfer M 15 (Pneumatic trench mortar) was a light mortar used by Austria-Hungary in World War I. Remarkably it was not designed by an arms manufacturer but by personnel of the 58th Infantry Division; the first twenty examples were built in the division's workshops. Production was later contracted out to Vereinigte Elektrische Maschinen AG (United Electrical Machinery AG) in Budapest. The method of operation is usually described thus:

"It used the breakable screw method to retain the bomb in place until the air pressure in the chamber was strong enough to break the screw. Grooves of different depths could be used to vary the range. It was sometimes referred to as the Roka-Halasz system."

Thedescription leaves much to be desired. It is not clear if the grooves are in the projectile or the barrel, and unclear how the depth of groove would affect the breaking stress of what was presumably some sort of set-screw that had to be screwed in for each round. This would not make for a rapid rate of fire. Presemably if you ran out of screws you were, well, screwed.

The use of this breaking-screw system seems a bit more logical when you consider that it appears to make a separate air reservoir unnecessary, which would much reduce the total weight of the weapon. In the picture it appears that the compressed-air cylinder is used as a stabilising weight instead.

The 86mm pneumatic mortar does not appear to have a Wikipedia page.

THE AUSTRIAN 10.5 cm PNEUMATIC MORTAR

The 10.5 cm Luftminenwerfer M15 was a medium mortar was developed by the German firm of Ehrhardt & Sehmer. it was muzzle-loading and had no recoil system. Each cylinder of compressed air was good for fifteen shots.

A batch of 25 mortars, 250 air cylinders and 10,000 bombs with fuses was ordered on 31 July 1915 for trials in the field, but Ehrhardt & Sehmer proved to be unable to deliver the mortar bombs, and these manufactured by the Army itself. A slightly improved model was offered by Ehrhardt & Sehmer at the end of March 1916, but it was rejected because of the lack of effectiveness of the ammunition, difficulty in procuring it, and its poor range. Ten trench mortar platoons, each with two mortars, were formed and deployed in February 1916, mainly to the Eastern Front.

Ehrhardt & Sehmer of Saarbrücken made a large variety of machinery. After severe war damage in 1945 the company was still around for its 75th anniversary in 1951.

This pneumatic mortar has a Wikipedia page, but no picture of it has so far been found.

THE AUSTRIAN 12 cm PNEUMATIC MORTAR

Left: 12cm pneumatic mortar: 1916

The long-barrelled pneumatic mortar in the foreground is displayed in the Museum of Military History at Vienna. (Well worth a visit) It was described as the 'Luftminenwerfer M16' ie, Pneumatic mine thrower, Model 1916.

The barrel is 2 metres long and the bore is 12 cm. The compressed air was stored in a cylinder at 35 atmospheres; (514 psi) a full cylinder of compressed air would deliver eleven shots.Two projectiles can be seen on the wooden board in front of the mortar. Circular studs are fitted at the rear end of each round. Assuming this device works in the same way as the 20cm air mortar, they engage in grooves in the breech section that give the shell rotation as it accelerates; the barrel itself is smooth-bore. There is no recoil system, the barrel was rigidly mounted. This may have only been practical because of the relatively gentle acceleration of the projectile by the compressed air.

The 12cm pneumatic mortar required a crew of three.

Author's photograph

Left: 12cm pneumatic mortar: 1916

This is a close-up of the breech section. The details of operation are still being researched, but it appears that the breech swung open on a hinge at the left side of the two bright-metal rings, to allow insertion of the shell. The fitting on the left of the breech appears to be the compressed-air inlet. The release of the projectile was presumably initiated in some way by striking the dome-headed plunger at the back of the breech; the function of the adjacent rotating arms is currently unknown.

An obvious question (not yet answered by the Museum research team) is where the compressed air came from. A pressure of 514 psi is not going to be achieved by any sort of hand-pump in a reasonable time, and it does not seem advisable to site a petrol-motor-driven compressor in the front line with the mortar; it would be noisy and attract all sorts of unwanted attention, and destroy the main advantage of a pneumatic mortar- its relative quietness and lack of betraying smoke. The conclusion has to be that the compressed air cylinders were filled in a rear area and then carried up to the point of use. Ammunition obviously had to be carried up, but the need to lug air cylnders about as well probably meant that this weapon was not popular with the troops that had to supply it.

The 12cm Luftminenwerfer M16 has its own Wikipedia page.

Author's photograph

Left: Austrian 12cm pneumatic mortar: 1915

A contemporary picture of the 12 cm mortar with the breech open.

THE AUSTRIAN 15 cm PNEUMATIC MORTAR

This pneumatic mortar was developed by Maschinenfabrik Esslingen for German use. Austria acquired a batch of five for testing. Evaluation in September 1915 was positive, and four of them were deployed in combat trials at the end of October 1915

No photograph or drawing has so far been unearthed, but it is thought the barrel had a full 360° of traverse on a base plate. One cylinder of compressed air was adequate for twelve discharges.

There was a Model II incorporating minor improvements suggested by both Austrian and German pioneer troops, which was evaluated at the end of 1915. Two hundred were ordered, but the mortar was rendered obsolete by the superior performance of the 12 cm Luftminenwerfer M 16 before production was finished, and the design was shelved.

The 15cm Luftminenwerfer M15 has its own Wikipedia page.

THE AUSTRIAN 20 cm PNEUMATIC MORTAR

Left: Austrian 20cm pneumatic mortar: 1916

The 20 cm Luftminenwerfer M16 was the largest pneumatic mortar used by the Austrian army.

According to the Osprey book 'The Austro-Hungarian Forces in World War I (2): 1916-18' the working pressure was 55 atmospheres (808 psi)and it could throw either 50lb or 76lb projectiles to a range of about 1150 metres. It weighed a hefty 1600lb and was normally operated by a crew of five men. The air canister below the breech had to be replaced for each shot, bringing the maximum rate of fire down to one round every six minutes. This is slooow.....

These mortars were by no means silent in operation, which made all the compromises in their operation very questionable. They are described as giving a distinctive 'cough' that gave warning they had been fired, and some time to take cover.

The 20cm Luftminenwerfer M16 has its own Wikipedia page.

THE HOLMAN PROJECTOR: 1940

The Holman Projector was a low-altitude anti-aircraft weapon used by the British Navy during the Second World War. It was defensive weapon for British merchant ships, against low-level attacks. Its range was short and accuracy poor but it could put up a large volume of fire which effectively deterred enemy pilots.

Left: A Holman projector being prepared for initial trials on land: 1940

Dropping a round down the smooth (unrifled) barrel activated an air supply from high-pressure cylinders. Each air cylinder could fire fifty rounds, which sounds like a considerable advance on the WW1 pneumatic mortars.

The ring affair attached to the end of the barrel is a very crude anti-aircraft sight.

A Mk2 version that used steam for propulsion, from the ship's boilers, was later introduced. This eliminated the need to have a compressed-air system on the vessel.

A total of about 4,500 Holman Projectors were put into action during World War II. They were considered very successful.

The Holman Projector has its own Wikipedia page.

MODERN PNEUMATIC GUNS

Today we have the Light-Gas Gun as a research tool rather than a weapon. The NASA gun referred to there works very much like a Sims-Dudley, using gunpowder to compress hydrogen which spits a small projectile out of the barrel at up to 6000 m/s. Note that a bursting-disk is used to delay launch until the pressure has suitably built up.

On the other hand, the Combustion light-gas gun is intended as a weapon. The projectile is propelled by the combustion of hydrogen or methane, so it does not really count as a pneumatic weapon since the driving force is not stored pressure.

Left: Preparing to launch a Jaguar off the deck of HMS Invincible: 2003

This was a part of the Top Gear saga, in which a Stig was supposedly killed off while attempting to race a Harrier jumpjet down the flight deck. In fact the car was shot off the edge of the deck by a nitrogen cannon.

The gas cylinders visible at left are grey with a black top, which is the international code for nitrogen. The cylinders are used to charge the pressure vessel in the foreground, making a large amount of gas available for immediate supply to the piston which shoves the car into the ocean.

You can see the (carefully edited) result on YouTube.

Photograph by kind permission of Bill Todd.

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