Part 30
The shotgun and rifle, the familiar weapons of the sportsman and the foot-soldier, are not the ancestors of the cannon, as might be surmised. On the contrary, the cannon was the predecessor of the musket and its successors. The rifle, however, antedated the rifled cannon, the type of modern artillery. We do not know when cannon first appeared, but it may have been soon after the discovery of gunpowder in Europe. This explosive seems to have been known in China long before knowledge of it reached the west, but we do not know to what extent it was developed and used in that country.
The earliest cannon of which we have any knowledge were clumsy contrivances, at first wider at the mouth than at the chamber, and made of wood, and later of iron bars, hooped together with iron rings, a system of the same type as that now in use in the wire-wound cannon. They at first seem to have fired balls of stone, iron balls coming later. A doubtful statement exists to the effect that cannon were used at the siege of Belgrade in 1073, and it is said that Edward III used them against the Scotch in 1327. Other dates of their use are 1338 and 1346, in which latter year Edward III employed them against the French at Crecy. For this we have the authority of Froissart. They were known under the varied names of bombards, serpentines, etc. Twelve cannon cast by Louis VII were named after the twelve peers of France, and Charles V gave twelve others the names of the twelve apostles. Other titles came later into general use, the royal or carthorne, carrying 48 pounds; the culverin, 18 pounds; the demi-culverin, 9 pounds; the basilisk, 48; the siren, 60, etc. In still later times cannon became known by the weight and the balls they carried, 6-pounders, 12-pounders, etc. But they are now usually called after the size of their bores, as 6-inch, 8-inch, or 12-inch cannon. The oldest example still in existence is “Mons Meg,” preserved at Edinburgh Castle. This is one of the iron-bar type, hooped by iron rings. It is supposed to have been used by James II of Scotland, at the siege of Threave Castle in 1455.
Louis VI used bombards of great length and power against the Flemish in 1477, while as early as 1401 bronze cannon had been cast in several cities of West Prussia. Iron cannon were not cast until near the end of that century. Coming down to the seventeenth century, we are told of the great Bijapur cast-iron gun, the “Lord of the Plain,” cast by the Mogul emperor Auremgzebe or by his foes the Mahrattas. This huge gun was 14 feet long, 28 inches bore, and fired a ball of 1,600 pounds weight. Smooth-bore cannon and mortars of cast-iron and bronze are still retained in some fortresses, though rifled cannon are the only type now made. As late as 1864 smooth-bore 100- and 150-pounder wrought-iron guns were made for the British navy and a few bronze rifled guns were made in 1870 for service in India, but all such guns are now obsolete.
The development of the rifle from the old smooth-bore musket, by cutting grooves or channels in the form of a screw in the interior surface, was found so advantageous in increase of precision of aim and length of range, that the rifling of cannon in time followed and is now universally used. Breech loading has also replaced muzzle loading, another vast advantage in the use of artillery. A form of breech-loading cannon was introduced in the sixteenth century, but the advantageous use of this device is of late invention. An important result of these changes is the use of elongated instead of round balls, this permitting of the employment of much heavier projectiles for the same width of bore.
Modern Cannon.
Until 1888 the largest cannon in use was the 119-ton Krupp, made in 1884 for Italy; but in 1888-90 the same house produced a 135-ton gun for Cronstadt. The heaviest British gun at that time was of 111-ton weight. This threw a projectile of 1,800 pounds with a muzzle velocity of 2,216 feet per second. But there later came a reaction in favor of lighter guns and quick firers. The heavy cannon of recent times are not cast, as of old, but are made of forged-steel by what is known as the building-up process. The different parts of these are called the tube, jacket, hoops, locking rings, trunnion rings, wire winding, etc.
Cannons are subject to great stress in firing, this being of two kinds. One is the longitudinal stress, acting in the direction of the length and tending to pull the muzzle away from the breech. The other is the circumferential or tangential stress, which tends to split the gun open in lines parallel to the axis of the bore. These stresses are results of the longitudinal and radial pressures of the gas developed by the ignition and explosion of the powder. Such destructive forces have to be guarded against in the building of a cannon and have led to a great development over the old-time casting processes. As long as projectile velocities under 1,500 feet per second were employed cannons cast in one piece sufficed, but when greater velocities were sought, the pressure grew so extreme that no cast or forged metal tube would stand the strain.
How Cannon are Now Made.
It was found that the inner surface of the tube stretched more than the outer surface, and that after the inner surface had been stretched to its limit of elasticity the outer part failed to add to its strength, so that further thickness was of no benefit. To do away with this condition cannon were constructed on the principle of varying elasticity, the metal with the greatest elongation within its elastic limit being placed next to the bore, yet in high-powered guns this system failed to yield the result desired and it was replaced by what is known as the initial tension system. This comprised two methods: the plain built-up gun and the wire-wound gun. In the latter certain parts of the gun were wrapped with wire in the form of a ribbon.
Built-Up and Wire-Wound Guns.
A built-up gun is made of several layers of forged steel. The parts of such a gun are known as the liner, the tube, the jacket and the hoops. The liner is a single piece which extends the length of the bore and is intended to contain the rifling and the powder chamber. This is inclosed by the tube, which is also in one piece, surrounding the liner throughout its length. Outside this is the jacket, made in two pieces and shrunk on the tube. Over the jacket lie the hoops, six or seven of these being used in a big gun. Like the jacket, these also are shrunk on. All these parts are made of the finest quality of open-hearth steel.
These pieces are prepared with the utmost care to prevent any defective material entering into the make-up of the gun. After the parts are put together a thorough forging follows, either by use of hammer or press, the latter being now used in preference. The usual practice in forging is to continue it until the ingot is decreased to one-half its original thickness and is within two inches of the desired diameter of the finished work. It is then annealed with great care to relieve the strains set up in the metal by the forging and next goes to the machine shop to be rough bored and turned. The final boring takes place after a second annealing. The above is only a rapid sketch of the total process, in which elaborate care is taken to prevent imperfection of any kind.
In a wire-wound gun an inner tube of steel is thoroughly wrapped by successive layers of ribbon wire, each layer being wound with wire at a different tension. This type of gun is preferred by foreign manufacturers, but within the United States the built-up system is in higher favor and is almost exclusively employed. The makers of the wire-wound cannon claim for it a positive soundness of material impossible to secure in a built-up gun, and that it has greater firmness of material and superior tangential strength. But with this come certain disadvantages, a notable one being a lack of rigidity in the longitudinal direction, this tending to increase the “droop” of the muzzle and give a certain “whip” to the piece when fired that reduces accuracy. This and other disadvantages have given the built-up guns general preference in this country, they being found strong enough to bear any pressure desirable in service. In addition they are much cheaper to build than the wire-wound guns.
Modern heavy guns are made of medium open-hearth carbon steel, forged as stated. The liner and tube are then placed upright in an assembling pit, the jacket and hoops shrunk on, and the finishing work done, as above said, the breech mechanism being finally fitted. Within recent years there has been a steady increase in the size and range of cannon, until an immense size and weight have been attained. For naval purposes the 14-inch gun is the largest now used in American battleships, but in the United States coast defense forts, 16-inch guns are installed. England has equipped several of her latest battleships with 15-inch guns and other nations are following in the same direction. In recent great battleships four turrets are used, each carrying three of these great guns, giving a broadside of twelve of these monster weapons of war. Of the three guns, the middle one is raised above the line of the others. A battleship thus armed is able to fire six guns ahead and six astern by raising the second and third turrets so as to fire over the others.
Military cannon are divided into three classes, based upon the length of caliber, and technically known as guns, mortars and howitzers. In guns the length is relatively great, in mortars relatively small, compared to their calibers. Howitzers form a class between guns and mortars in length. The field guns of the American army are the 3.6-inch breech-loading mortars, and the 3.6-inch heavy and 3.2-inch light guns. The siege guns in the service are the 5-inch siege guns, the 7-inch howitzer, and the 7-inch mortar. The coast defense artillery consists of the 8-, 10-, 12- and 16-inch guns and the 12-inch mortars. In the recent European war very heavy cannon were used for field service, pieces of the size usually placed in forts being drawn to the field by powerful tractors, set on concrete platforms and used in attacks on fortified cities. It was through the use of such ordnance that the German army so easily reduced the strongly fortified Belgian cities.
(See page 410.)]
The range of these giant cannon is enormous and their destructive power great, this being added to by the fact that the explosive shell has replaced the solid round shot of old-time gunnery. A 14-inch gun of 45 caliber can discharge a 1,400-pound projectile at a muzzle velocity of 2,600 feet per second. If we compare this with a locomotive going at the speed of sixty miles an hour, we have in the latter a speed of eighty-eight feet per second to compare with the 2,600 feet per second of the cannon ball. From this we can well conjecture the vast speed with which the latter moves, its enormous range and vast powers of destruction.
As facts are better than theories, it will be of interest to adduce a recent example of gunnery of a most illuminating type, but as regards distance and remarkable accuracy of aim. In September, 1916, the American battleship “Pennsylvania,” armed with a main battery of twelve 14-inch guns, fired these simultaneously at a target in the Chesapeake 22,000 yards, or more than twelve miles, away. The target was the sunken hulk of the “San Marcos,” formerly the battleship “Texas,” which for several years had been used for similar purposes. As the target was invisible to the gunners it was hardly to be expected that any of the shots should fall near the target. But the extraordinary result appeared that five of these twelve shots struck the hulk. As each of these projectiles weighed 1,400 pounds any battleship receiving such a broadside would probably have gone promptly to the bottom. The result, which has never before been equaled in accuracy, sufficiently attests the remarkable proficiency in range-finding that modern engineers have developed.
As for the penetrating powers of such huge shot we may take the 15-inch gun, the type of the largest guns in our fortifications and which is claimed to be able to pierce sixteen inches of armor at a range of 18,000 yards and ten inches at a range of 20,000 yards. A notable example of this took place on September 15, 1916, at the proving grounds at Indian Head, on the Potomac River, when a 16-inch, 2,100-pound, solid steel shell, said to be the first ever fired from a naval gun of that caliber, with a small charge of explosive, went through a plate of armor, penetrated a thick sand backing, and continued its course, striking the house of an employee of the proving grounds and plunging through the kitchen rending all before it. This was a naval gun, the largest yet made for naval purposes.
In the make-up of modern guns the breech-loading mechanism is of essential importance, it being necessary that the breech should be capable of rapid opening for the insertion of the charge into the loading chamber, as rapidly closed and firmly secured to prevent it being forced open by the reaction of the discharge. It also must fit with such tightness as to prevent any escape of the gas in that direction, and force it to exert all its impelling power upon the ball. Various methods are used for this purpose, with the result that loading and firing can be very quickly and effectively performed. In the case of guns in fortifications, the disappearing carriage is a highly important invention of recent date. By its aid the gun is quickly lifted to fire over the walls of the fort and is driven backward by the force of its discharge, sinking to a place of safety behind the walls. This saves the gun and its crew from injury by return fire.
We may say in conclusion that the great European war was notable for the use of artillery to an extent far surpassing its employment in any previous war. This great conflict, indeed, was very largely a contest of gun fire, in which the opposing fields of the battling armies were so swept with shells and other explosives as to render life impossible on the open land, trench digging being one of the main employments of the embattled hosts. Never before had the supreme value of gunnery in warfare been so fully demonstrated.
AMMUNITION. (See page 402.)