Sunday, 15 March 2009

Gun construction in wrought iron and bronze

It seems probable that the first material used in making guns was a copper alloy similar to brass or bronze. The earliest guns in the Royal Artillery Museum are Chinese and, although one of them is an early cast iron, the other is a copper alloy piece of a type that seems to have been made for many years - it even has a production number.

These copper alloys are easier to work than iron, which requires a higher melting temperature in order to make cast iron or a skilled blacksmith for wrought iron. Casting in copper is relatively straightforward and needs little imagination, but we will come to that presently. Let's start with wrought iron.

In Europe in the days before iron could be melted, it was worked by heating it to a glowing red and hammering it on an anvil. That is how horseshoes are made and the procedure for making guns followed the same path. Manufacture began with a sheet of iron that had been hammered out from a block and then wrapped around a mandrel - a solid cylindrical block of the required calibre for the gun itself. This formed the inner 'tube' or lining of the gun. Long rods of iron made like staves were then laid out along the length of the gun and held in place by a series of iron hoops. These were slipped into place while still hot, so that as they cooled and shrank, they tightened the rods in place. This built-up construction produced a tube open at both ends. Onto one end was fitted a 'breech block', often in the shape of a beer mug, complete with a handle and a vent hole. Holding that in place was usually a suitably shaped mounting carved out of a solid block of wood, while the rest of the gun was strapped tightly to that same mounting.

This construction, using long staves and hoops, was very similar in concept to the cooper's method of making wooden casks. Another name for a cask is a barrel - hence the name 'barrel' for the long tube of a gun!

This method of making guns was extremely laborious and the guns themselves tended to leak gas pressure, especially around the breech area, and were frequently not strong enough, blowing apart and injuring the gunners who served them.

Casting guns in copper was much preferred, though copper itself was expensive and had to be imported into England from the Continent. The skills also had to be imported and it was Henry VIII who had the wealth and determination to do just that, persuading a Venetian gunfounding family, the Arcana, to come to England and start making guns for the King. The procedure was relatively simple in concept, if rather more complex in practice.

It began with the making of a maquette - an exact replica of the external dimensions of the gun, complete with decoration (see picture), made in clay. This was actually made on a former - a length of wood wrapped in coils of thin rope, then covered in clay. When the maquette had dried, it was lightly greased and then the mould was built up around it in clay. When this, too had dried, the maquette was broken out of the mould - this was where the rope coils came in, since these could easily be pulled out, together with the former, leaving just the relatively thin clay to be broken away.

The mould was then thoroughly dried before being buried in a casting pit, muzzle end upwards, for the molten metal to be poured into it. In the years before the late 18th Century, a metal rod would be placed inside the mould and secured so that the molten metal would run around it, forming the inner shape of the barrel. However, it was found that casting the piece as a solid and drilling out the bore of the gun produced a stronger barrel.

Thursday, 12 March 2009

Artillery Ammunition - Part 1: Smoothbore period

The real weapon of the artillery is the bit that does the damage, i.e. the ammunition, not the gun or mortar though, of course, the rocket is both the projector and the ammunition.

The earliest ammunition types were the war arrow, a hail of large stones and the stone cannonball. It would be difficult to say which came first, though the war arrow is the munition depicted in the earliest known image of a gun.

There seems to be no record of them being used in war, but they remained in the inventory of the Tower of London for some 200 years. They would have had to have the warhead and the fins of the same diameter as the bore of the gun and be loaded with a tampion or wad between the tail and the propellant to provide the seal that allowed the propellant to develop its pressure. Their disadvantage was that they were only effective against men or cavalry in the open and did not have the 'hitting power' of a cannonball in siege warfare.

The hail of stones was a weapon of the 'perrier' mortar and was useful in sieges for attacking people in the open, thinking themselves protected by city or fortress walls. The stone cannonball was really only a replica of the projectiles hurled by the catapult and trebuchet, but in guns it had to be cut more accurately if it was to do the job of sealing the propellant gases long enough for them to build up pressure, and of course, not to damage the gun.

When guns began to be cast in bronze, there were occasional examples of bronze cannonballs, but the more usual early shot from these guns was the stone ball with a covering of lead. The lead gave it the weight to make it carry further and yet avoided the problems in making it entirely of lead and too heavy. Too much weight produces greater resistance in the bore and could result in bursting the gun.

Once the technique required for melting iron had been discovered, guns were cast in this material, producing stronger guns that could cope with heavier ammunition and larger propelling charges. Cannonballs began to be made of iron, usually by the same people who were casting iron guns because they had both the material and the requisite skills.

Throughout the early period and right up to the end of the smoothbore period in the middle of the 19th Century, incendiary projectiles were much in evidence. They were used in siege warfare to set fire to the wooden constructions and thatched roofs found inside cities and castles. Based on a simple internal framework, the materials used to construct the fireball varied over the years, but they must have been a frightening sight for the defenders as they flew across the sky, flames burning brightly and trailing smoke.

The invention of the hollow shell led to the development of other types of ammunition. Filled with gunpowder and detonated by a long fuze, shells were very effective in causing both damage and casualties. The blast effect, with its noise and the flying fragments of the burst shell, was a new terror both in siege warfare and on the battlefield. When Henry Shrapnel packed a shell with musket balls and burst the shell above the heads of the enemy, the rain of lead balls was, in effect, a longer range version of 'canister', the dreaded hail of lead fired at close range against infantry and cavalry.

And last, the extraordinary invention of light-producing flares to illuminate the battlefield or the breach in a siege wall, including during the 19th Century a flare packed with a parachute that would take longer to fall, making it more useful.

Thursday, 5 March 2009

What's the connection between artillery and spiders?

Strange as it may seem, there is one and it's even written up in an official 20th Century pamphlet on artillery instruments.

Put very simply, spiders spin a tough silken thread that makes an excellent 'graticule' in an optical sight, such as those used in artillery instruments. Graticules are the fine lines in a sighting system that are used to lay an instrument accurately on a given point. It was found that the web of a common spider in the grounds of the Royal Arsenal could be used, and these were sought out so that long strands could be selected and wound on a frame. A short length would then be sandwiched between thin sheets of optical glass and inserted at the correct point in the lens system for the sight so that it would remain in focus when the sight was being aimed, whether at a close or a distant object.

I doubt whether it's a system still in use, though graticules remain an essential element of many types of sight and of military binoculars and telescopes. Spiders are probably considered old-fashioned - a bit like gravity, but that's another story!

Wednesday, 4 March 2009

Artillery Instruments

One of the most basic instruments used in artillery is that for determining the elevation angle of a gun. It was known from the earliest experiments with guns that a given angle of elevation together with a fixed amount of propelling charge would achieve (theoretically!) the same trajectory every time the gun was fired. Variations in the quality of the propellant, the weight of the projectile, the condition of the bore, the weather conditions etc. all affected this trajectory, but for their purposes, gunners were able largely to rely on this angle of elevation to achieve a known range.

It was therefore important to be able to set this angle on the gun. Their solution was the gunner's quadrant. This simple device had an arm that went into the barrel, a quarter circle (quadrant) measuring instrument and a plumb bob. As the gun elevated, so the plumb bob's string moved on the quadrant, allowing the gunner to read the angle.

Over time, of course, this device became gradually more sophisticated, acquiring a levelling bubble to replace the plumb bob and achieving very high accuracy by the means of precision engineering. However, in essence, that is all that a gunner's quadrant is - a means of measuring the angle of elevation of a gun's barrel.

Sunday, 1 March 2009

Concentrating Fire

After the major changes that took place in artillery at the end of the 19th Century - improvements in ammunition effectiveness, in range and accuracy, in survey, in communications and in the relatively new art of indirect fire - gunners began to use the new capabilities to concentrate fire.

In essence, this meant bringing down artillery fire on a target from more than a single battery. Now that they had the communications to pass target details to other batteries, it became possible to engage a target with every battery in range. The more that ranges improved, the more batteries it became possible to concentrate on a given target.

This in turn drove the pressure for further improvements in communications, with telephone lines and radio frequencies dedicated to artillery use, and procedures for command and control that established the priorities to be followed in engaging targets.

Survey methods were developed that put all batteries on the same 'grid' - i.e. knowing exactly where each one was in relation to all the others - and ensuring that they had a common 'orientation', so that when their sights were pointing at 'grid north', for example, all guns were parallel. When this was achieved, it became possible for one battery to be adjusted onto a target and any adjustments to the 'map bearing and range' by the 'ranging battery' could be applied to the map bearing and range of any other battery.This meant in effect that any other battery within range could engage the target without further adjustment. This not only saved time and ammunition, but provided no warning to the target about how many guns were about to engage it.

I have simplified the process to its essentials: it was in practice rather more complicated, but it was a major factor in World War 1, the first 'artillery war'. The stalemate of the trenches made attacking across the no man's land between them a deadly lottery. Artillery was needed to suppress enemy firepower whilst infantry crossed in the open to come to grips with their opposition. Complex fire plans were evolved, tasking batteries to engage targets in preparation for an attack, sometimes for days at a time, pounding at defences in an attempt to weaken strongpoints, cut barbed wire and crush morale. This preliminary bombardment would be followed by firing at specific targets at set times to coincide with infantry movement, aiming to keep the enemy's infantry hiding under cover while the attack developed across open ground. Batteries would then 'lift' to engage targets in rear of the front lines, aiming to break up counter-attacks and to suppress enemy batteries.

One of the new methods of fire involved 'creeping barrages', with the supporting fire falling in lines just in front of the advancing troops and lifting line by line as little as 50 yards ahead of the infantry. These barrages were immensely complicated to work out and to achieve, but they were nonetheless a useful aid in keeping the infantry moving in the right direction in the fog of war and in preventing the enemy machine-gunners from mowing down the unprotected infantry.

By the time of World War 2, the Allied firepower was so great that they could afford to hit anything that moved with devastating effect. This led to rapid advances in the closing year of the War as the German armies were forced back across north west Europe. The lesson was rammed home again in the first Gulf War: concentrated artillery firepower remains the Queen of the Battlefield.