Cannon
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For other uses, see Cannon (disambiguation).
A cannon is a type of artillery, usually large and tubular in shape, that uses gunpowder or other explosive-based propellants to launch a projectile over a distance. Cannon vary in caliber, range, mobility, rate of fire, and fire power; different types combine and balance these attributes in varying degrees, depending on their intended use. First used in China, cannon were among the earliest forms of gunpowder artillery. The first cannon in Europe probably appeared in Iberia, during the Islamic wars against Spain in the 12th century. English cannons were first used during the Hundred Years' War at the Battle of Crécy, in 1346. The end of the Middle Ages saw the introduction of a more standardized and effective cannon. Some of the largest cannon ever constructed were of Asian origin, such as the Indian Jaivana cannon. Some European pieces were also large, but were abandoned in favor of greater numbers of lighter, more maneuverable ones; this eventually lead to the use of modern field artillery. While the medieval Great Turkish Bombard required two hundred men to operate, 18th century English cannon required only a dozen men, including two gunners; by the Napoleonic Wars, only five men were needed to operate an English cannon.
Etymology and terminologyImage:Jaivana.jpg
The Jaivana cannon is the largest wheel-mounted cannon in the world.
"Cannon" is derived from the Old Italian word cannone, meaning "large tube," which came from the Latin canna, in turn originating from the kanna,—Greek for "cane," or "reed"—and ultimately deriving from the Akkadian term qanu, meaning "tube" or "reed."[1][2][3] The word "cannon" has been used to refer to a gun since 1326, in Italy, and 1418, in England. Bombardum, or bombard, was the earliest-used word for "cannon," but came to refer only to the largest weapons after 1430.[4] "Cannon" serves both as the singular and plural of the noun, although the plural "cannons" is also correct.[1] Any large, smoothbore, muzzle-loading gun—used before the advent of breech-loading, rifled guns—firing explosive shells may be referred to as a cannon, though the term specifically refers to a gun designed to fire a 42 lb (19 kg) shot, as opposed to a demi-cannon—32 lb (15 kg)—culverin—18 lb (8.2 kg)—or demi-culverin—9 lb (4.1 kg). When on board a warship, a cannon is usually called a "gun," while a cannonball is referred to as a "roundshot."[5] The term cannon also applies to the autocannon, a modern gun with a caliber of 20 mm or more. Autocannon have been used extensively in fighter aircraft since World War II, and are sometimes used on land vehicles as well.[6][7] History
Image:FireLanceAndGrenade10thCenturyDunhuang.jpg
Earliest known representation of a firearm (a fire lance) and a grenade (upper right), Dunhuang, 10th century.[8]
One of the earliest known cannon was invented by Ctesibius of Alexandria, before 200 BC.[9] Primitive, it operated using compressed air, rather than gunpowder.[10] One of the first cannon used in the military was the fire lance, a gunpowder-filled tube attached to the end of a spear and used as a flamethrower.[11] Shrapnel was sometimes placed in the barrel, so that it would fly out along with the flames.[12] Eventually, the paper and bamboo of which fire lance barrels were originally constructed came to be replaced by metal.[13] The earliest known depiction of a firearm is a sculpture from a cave in Sichuan, dating to the 12th century, that portrays a figure carrying a vase-shaped bombard, firing flames and a cannonball.[14][13] The oldest surviving gun, dated to 1288, has a muzzle bore diameter of 2.5 cm; the second oldest, dated to 1332, has a muzzle bore diameter of 10.5 cm.[11] Image:Yuan chinese gun.jpg
Hand cannon from the Chinese Yuan Dynasty (1271–1368).
The first documented battlefield use of gunpowder artillery took place on January 28, 1132, when Song General Han Shizhong used huochong to capture a city in Fujian. The first known illustration of a cannon is dated to 1326.[15] In his 1341 poem, The Iron Cannon Affair, one of the first accounts of the use of gunpowder artillery in China, Xian Zhang wrote that a cannonball fired from an eruptor could "pierce the heart or belly when it strikes a man or horse, and can even transfix several persons at once."[16] Joseph Needham suggests that the proto-shells described in the Huolongjing may be among the first of their kind.[11] The Chinese also mounted over 3,000 bronze and iron casted cannon on the Great Wall of China, in order to defend themselves from the Mongols. The weapon was later taken up by both the Mongol conquerors and the Koreans. Chinese soldiers fighting under the Mongols appear to have used hand cannon in Manchurian battles during 1288, a date deduced from archaeological findings at battle sites.[17] In the 1593 Siege of Pyongyang, 40,000 Ming troops deployed a variety of cannon to bombard an equally large Japanese army; the Japanese were defeated in one day. During the Seven Year War in Korea, both the Chinese-Korean coalition and the Japanese army used artillery widely, in both land and naval battles.[18] Middle East
Image:Great Turkish Bombard at Fort Nelson.JPG
The Great Turkish Bombard, a very heavy bronze muzzle-loading cannon, similar to those used by the Ottoman Empire in the Siege of Constantinople, 1453 AD.
Portable hand cannon ("midfa," in Arabic) were first used by the Egyptians to repel the Mongols at the Battle of Ain Jalut in 1260, and again in 1304.[19][20] The composition of the gunpowder used in these battles was later described in several manuscripts, written in the early 14th century. Four different mixtures were used, the most explosive having a composition (74% saltpeter, 11% sulfur, 15% carbon) almost identical to modern gunpowder (75% saltpeter, 10% sulfur, 15% carbon). These mixtures were more explosive than those used in either China or Europe during this period.[19][20] The Battle of Ain Jalut also saw the use of the earliest known gunpowder cartridges, employed by the Egyptians in their fire lances and hand cannon.[19] The use of cannon as siege machines dates back to Abu Yaqub Yusuf, who employed them at the siege of Sijilmasa, in 1274, according to Ibn Khaldun.[19] Also intended for siege warfare, the first supergun, the Great Turkish Bombard, was used by the troops of Mehmed II to capture Constantinople, in 1453. Urban, a Hungarian cannon engineer, is credited with the invention of the cannon.[4] It had a 762 mm bore, and could fire 544 kg (1,200 lb) stones nearly a mile away.[4] The Great Turkish Bombards were cast in bronze and made in two parts: the chase and the breech, which, together, weighed 16 tonnes.[21] The two parts were screwed together using levers to facilitate the work. Another weapon, fashioned for killing infantry, was the first multi-barrel machine gun. It was invented by Fathullah Shirazi (c. 1582), a Persian-Indian polymath and mechanical engineer, who worked for Akbar the Great in the Mughal Empire. As opposed to the polybolos and repeating crossbows used earlier in Ancient Greece and China, respectively, Shirazi's machine gun had multiple gun barrels that fired hand cannons loaded with gunpowder.[22] Medieval EuropeIn Europe, the first mention of gunpowder's composition in express terms appeared, in Roger Bacon's "De nullitate magiæ" at Oxford, published in 1216.[23] Later, in 1248, his "Opus Maior" describes a recipe for gunpowder and recognized its military use:
Bacon noted that firecrackers were "used in certain parts of the world." His mixture resembles the assumed composition of Chinese slow-burning powder,—such as those used in fire arrows, and rockets—but is not a good propellant, as the saltpeter content is too low.[25] Image:EarlyCannonDeNobilitatibusSapientiiEtPrudentiisRegumManuscriptWalterdeMilemete1326.jpg
Earliest picture of a European cannon, "De Nobilitatibus Sapientii Et Prudentiis Regum," Walter de Milemete, 1326.
The first use of gunpowder in Europe was the Moorish cannon, first used by the Andalusians in Spain, at the siege of Seville in 1248, and the siege of Niebla in 1262.[19][26] By 1250, "coal and sulfur" had been recognized as the best weapon for ship-to-ship combat,[27] while hand guns were probably in use on land. Italian scopettieri ("gun bearers") were mentioned in conjunction with crossbowmen, in 1281. In Spain, the "first artillery-masters on the Peninsula" were enlisted, at around the same time.[28][29] The first metal cannon was the pot-de-fer. Loaded with an arrow-like bolt that was probably wrapped in leather to allow greater thrusting power, it was set off through a touch hole with a heated wire. Such weapons were used by the French, and possibly the English, during the Hundred Years War, when cannon saw its first real use on the European battlefield.[30] Even then, cannon were still a relatively rare weapon. "Ribaldis," which shot large arrows and simplistic grapeshot, were first mentioned in the English Privy Wardrobe accounts during preparations for the Battle of Crécy, between 1345, and 1346.[31] The Florentine Giovanni Villani recounts their destructiveness, indicating that by the end of the battle, "the whole plain was covered by men struck down by arrows and cannon balls."[31] Similar cannon were also used at the Siege of Calais, in the same year, although it would not be until the 1380s that the "ribaudekin" clearly became mounted on wheels.[31] Around the same period, the Byzantine Empire began to accumulate its own cannon to face the Ottoman threat, starting with medium-sized cannon 3 feet (0.91 m) long and of 10 in caliber.[32] The first definite use of artillery in the region was against the Ottoman siege of Constantinople, in 1396, forcing the Ottomans to withdraw.[32] They acquired their own cannon, and lay siege to the Byzantine capital again, in 1422, using "falcons," which were short but wide cannon. By 1453, the Ottomans used 68 Hungarian-made cannon for the 55-day bombardment of the walls of Constantinople, "hurling the pieces everywhere and killing those who happened to be nearby."[32] The largest of their cannon was the Great Turkish Bombard, which required an operating crew of 200 men[33] and 70 oxen, and 10,000 men to transport it.[32] Gunpowder made the formerly devastating Greek fire obsolete, and with the final fall of what were once the strongest walls in Europe on May 29, 1453, "it was the end of an era in more ways than one."[32] Early modern periodBy the 1500s, cannon were made in a great variety of lengths and bore diameters, but the general rule was that the longer the barrel, the longer the range; some cannon made during this time could have barrels exceeding 10 feet in length, and could weigh up to 20,000 lb (9,100 kg); large amounts of gunpowder were needed to allow them to shoot a stone ball up to over three hundred yards.[34] By mid-century, European monarchs began to classify cannon to reduce the confusion. Henry II of France opted for six sizes of cannon,[35] but others settled for more; the Spanish used twelve sizes, and the English sixteen.[36][37] Better powder had been developed by this time as well. Instead of the finely-ground powder used by the first bombards, powder was replaced by a "corned" variety of coarse grains. This powder, being irregularly distributed, had pockets of air between grains, allowing fire to travel through, and ignite the entire charge quickly and uniformly.[37] The end of the Middle Ages saw the construction of larger, more powerful cannon, as well their spread throughout the world. The Tsar Cannon, founded by Russian founding master Andrey Chokhov in 1586, is the largest howitzer ever made.[38] The cannon, which still survives today, was intended to fire grapeshot, and to defend the Kremlin, but was never used. In fact, with its large size, it may have been intended as a showpiece of military might and engineering, rather than for battle. Innovations continued, notably the German invention of the mortar, which was a thick-walled, short-barreled gun that blasted shot upward at a steep angle. Mortars were useful for sieges, as they could fire over walls, and other defenses.[39] This cannon found more use with the Dutch, who learned to shoot bombs filled with powder from them. However, setting the bomb fuse in the mortar was a problem. "Single firing" was the first technique used to set the fuse, where the bomb was placed with the fuse down against the propelling charge. Unfortunately, this practice often resulted in the fuse being blown into the bomb, causing it to blow up in front of the mortar. Because of this danger, "double firing" was developed, where the fuse was turned up and the gunner lighted the fuse and the touch hole simultaneously. This, however, required much skill and timing, and was especially dangerous when the gun failed to fire, leaving a lighted bomb in the barrel. Not until 1650 was it accidentally discovered that double-lighting was a superfluous process: the heat of firing was enough to light the fuse.[37] Siege engines, such as siege towers and trebuchets, became vulnerable and obsolete with the development of large cannon, and the resulting changes in fortification. However, wooden "battery-towers" took on a similar role as siege towers in the gunpowder age, such as that used at siege of Kazan in 1552, which could hold ten large-caliber cannon, in addition to 50 lighter cannon.[40]
Fort Bourtange, a star fort, was built with angles and sloped walls specifically to defend against cannon.
Wheeled gun carriages became more common by the end of the 15th century, and, as a result, field artillery began to emerge.[41] In The Art of War, Niccolò Machiavelli observed that "small pieces of cannon... do more damage than heavy artillery. The best remedy against the latter is making a resolute attack upon it as soon as possible..."[42] As was the case at Flodden in 1513, the English field guns outpaced the Scottish siege artillery, firing twice, or even thrice, as many rounds.[41] Later, Gustavus Adolphus emphasized the use of light cannon and mobility in his army. He trained three-man crews to fire his cannons and invented a special cartridge that contained both powder and shot to speed up loading. Additionally, he pioneered the use of canister shot against infantry, which was essentially a tin can filled with musket balls to kill infantry.[37] Around this time also came the idea of aiming the cannon to hit a target. Gunners controlled the range of their cannon by measuring the angle of elevation with a "gunner's quadrant." Cannon did not have sights, and even with measuring tools aiming was still largely guesswork.[37] Most notable in this period, however, is the effect of cannon on conventional fortifications. Machiavelli wrote, "There is no wall, whatever its thickness that artillery will not destroy in only a few days."[42] Although castles were not immediately made obsolete by cannon, their use and importance on the battlefield rapidly declined.[43] Instead of majestic towers and merlons, the walls of new fortresses were thicker, angulated, and sloped, while towers became lower and stouter; these new defenses became known as "star forts," after their characteristic shape.[43] Forts featuring cannon batteries were built during the Renaissance, such as the trace italienne of Italy, and the Tudors' Device Forts in England.[43] To guard against artillery and gunfire, increasing use was made of earthen, brick and stone breastworks and redoubts, such as the geometric star forts of the 17th century French Marquis de Vauban. These soon replaced castles in Europe, and, eventually, castles in the Americas were also superseded by bastions and forts.[44] 18th and 19th centuryThe lower tier of 17th century English ships of the line were usually equipped with demi-cannon, a naval gun that fired a 32 pound solid shot. Demi-cannon were capable of firing these heavy metal balls with such force that it could penetrate over a meter of solid oak wood, from a distance of 90 m (300 ft) back, and could dismast even the largest ships at close range.[45] A full cannon fired a 42 pound shot, but were discontinued by the 18th century, as they were too unwieldy. By the end of the century, principles long adopted in Europe specified the characteristics of the Royal Navy's cannon, as well as the acceptable defects, and their severity. The United States Navy tested guns by measurement, "proof by powder",—two or three firings—and used pressurized water to detect leaks.[46] The carronade was adopted by the Royal Navy in 1779; the lower muzzle velocity of the round shot when fired from this cannon was intended to create more wooden splinters when hitting the structure of an enemy vessel, as they were often deadly. The carronade was much shorter, and weighed between a third to a quarter less than an equivalent long gun; for example, a 32 pounder carronade weighed less than a ton, compared to a 32 pounder long gun, which weighed over 3 tons. The guns were, therefore, easier to handle, and also required less than half as much gunpowder as long guns mounted on naval garrison carriages, allowing fewer men to crew them.[47] Carronades were manufactured in the usual naval gun calibers,[48] but were not counted in a ship of the line's rated number of guns. As a result, the classification of Royal Navy vessels in this period can be misleading, as they often carried more cannon than were listed. The Great Turkish Bombards of the Siege of Constantinople, after being on display for four centuries, were used to battle a British fleet in 1807, in the Dardanelles Operation. The artillery hit a British ship with two 700 pound cannonballs, killing 60 sailors; in total, the cannon claimed over 100 lives, prompting the British to retreat. In 1867, Sultan Abdul Aziz gifted Queen Victoria the 17 ton "Dardanelles Gun," one of the cannon used at the siege of Constantinople.[33] In contrast to these antiquated weapons, Western cannon during the 19th century became larger, more destructive, more accurate, and could fire at longer range. One example is the American 3 in (76 mm) wrought-iron, muzzle-loading howitzer,—used during the American Civil War—which had an effective range of over 1.1 mi (1.8 km). Another is the smoothbore 12-pounder Napoleon, which was renowned for its sturdiness, reliability, firepower, light weight for a twelve-pounder, and range of 1,700 yards (1,600 m).[49] In the 1810s and 1820s, greater emphasis was placed on the accuracy of long-range gunfire, and less on the weight of a broadside. The carronade, although initially very successful and widely adopted, disappeared from the Royal Navy in the 1850s, after the development of steel, jacketed cannon, by William George Armstrong and Joseph Whitworth. Nevertheless, carronades were used in the American Civil War.[50] Image:Utah Battery San Juan Bridge.jpeg
U.S. troops fire during the 1899 Battle of Manila, Philippine-American War.
The practice of rifling,—casting spiraling lines inside the cannon's barrel—was first applied to artillery in 1855, giving cannon gyroscopic stability, and improving their accuracy. The Armstrong Gun—also invented by William George Armstrong—was adopted by the British military, only to be rejected soon after, in favor of the less expensive muzzle-loading cannon that had been in use before.[51] The cynical attitude towards recruited infantry in the face of ever more powerful field artillery is the source of the term "cannon fodder," first used by François-René de Chateaubriand, in 1814;[52] however, the concept of regarding soldiers as nothing more than "food for powder" was mentioned by Shakespeare as early as 1598, in Henry IV, Part 1.[53] The superior cannon of the Western world brought them tremendous advantages in warfare. For example, in the Opium War in China, during the 19th century, British battleships bombarded the coastal areas and fortifications from afar, safe from the reach of the Chinese cannon. Similarly, the shortest war on the record, the Anglo-Zanzibar War of 1896, was brought to a swift conclusion by shelling from British battleships.[54] 20th and 21st centuriesCannon in the 20th and 21st centuries are usually divided into sub-categories, and are not often called "cannon," but rather a more specific name. Some of the most widely used types of modern cannon are howitzers, mortars, guns, and autocannon, though a few superguns have been constructed. ArtilleryBy the early 20th century, infantry weapons became more powerful and accurate, forcing most artillery away from the front lines. Despite the change to indirect fire, cannon still proved highly effective during World War I, causing over 75% of casualties.[26] The onset of trench warfare after the first few months of World War I greatly increased the demand for howitzers, as they fired at a steep angle, and were thus better suited than guns at hitting targets on a horizontal plane, such as trenches. Furthermore, their shells carried larger amounts of explosives, and caused considerably less barrel wear. The German army took advantage of this, beginning the war with far greater numbers of howitzers than the French.[55] Mortars, smaller in caliber, but more accurate, were similarly prized during the Great War. Modern artillery is used in a variety of roles, depending on its type. According to NATO, the general role of artillery is to provide fire support, which is defined as "the application of fire, coordinated with the manoeuvre of forces to destroy, neutralize, or suppress the enemy." This defines artillery as being a supportive arm, though not all NATO armies agree it is.[56] Significant innovations have been made regarding the cannon's place in modern warfare. "Superguns" have been developed since the early 20th century, and the 20 cm (200 mm) caliber "Paris Gun" of World War I had the greatest range of a gun, achieving 122 km.[57] At the same time, the guns used aboard the Iowa class USS Wisconsin and USS Missouri were capable of firing projectiles a distance of 39 km (24 mi).[58] Testing has also been carried out on nuclear cannon in the 1950s, as in the United States' Operation Upshot-Knothole. Today, United States 152 mm artillery fires Shillelagh missiles, which are guided to their targets by infra-red beams, while the Super High Altitude Research Project artillery can fire shells 75.75 mi (121.91 km) above the earth's surface.[33] AutocannonAn autocannon is a cannon with a larger caliber than a machine gun, but smaller than that of a field gun. 20 mm (0.79 in) has remained the traditional minimum bore for autocannon since World War II, and, since they are the lowest caliber pieces, for all types of cannon as well. Autocannon have mechanisms to automatically load their ammunition, and therefore have a faster rate of fire than artillery, often approaching—and, in the case of Gatling guns, surpassing—that of a machine gun.[59] Most nations use these rapid-fire cannon on their light vehicles, replacing a more powerful, but heavier, tank gun. A typical autocannon is the 25 mm "Bushmaster" chain gun, mounted on the LAV-25 and M2 Bradley armored vehicles.[7] Autocannon have largely replaced machine guns in aircraft, due to their greater firepower.[6] The first airborne cannon appeared in World War II, but each airplane could carry only one or two, as cannon are heavier than machine guns, the standard armament. They were variously mounted, often in the wings, but also high on the forward fuselage, where they would fire through the propeller, or even through the propeller hub. Due both to the low number of cannon per aircraft, and the lower rate of fire of cannon, machine guns continued to be used widely early in the war, as there was a greater probability of hitting enemy aircraft.[6] However, as cannon were more effective against more heavily armored bomber aircraft, they were eventually integrated into newer fighters, which usually carried between two and four autocannon. The Hispano-Suiza HS.404, Oerlikon 20 mm cannon, MG FF, and their numerous variants became among the most widely used autocannon in the war. Nearly all modern fighter aircraft are armed with an autocannon, and most are derived from their counterparts from the Second World War.[6] The largest, heaviest, and most powerful airborne cannon used by the United States military is the GAU-8/A Avenger Gatling-type rotary cannon;[60] it is surpassed only by the specialized artillery pieces carried on the AC-130 gunship.[61] Although capable of generating a high volume of fire, autocannon are limited by the amount of ammunition that can be carried by the weapons systems mounting them. For this reason, both the 25 mm Bushmaster and the British 30 mm RARDEN are deliberately designed with relatively slow rates of fire, in order to extend the amount of time they can be employed on a battlefield before requiring a resupply of ammunition. The rate of fire of modern autocannon ranges from 90 rounds per minute, to 1,800 rounds per minute. Systems with multiple barrels—Gatling guns—can have rates of fire of several thousand rounds per minute; the fastest of these is the GSh-6-30K, which has a rate of fire of over 6,000 rounds per minute.[59] Such extremely high rates of fire are effectively employed by aircraft in air-to-ground and air-to-air combat, where the target dwell time is short, and weapons are typically operated in brief bursts. OperationImage:Cannoniere 1652.jpg
The parts of a cannon described, John Roberts, The Compleat Cannoniere, London 1652.
Cannon operation worked thusly: each cannon would be manned by two gunners, six soldiers, and four officers of artillery. The right gunner was to prime the piece and load it with powder, while the left gunner would fetch the powder from the magazine and keep ready to fire the cannon at the officer's command. Three soldiers stood on each side of the cannon, to ram and sponge the cannon, and hold the ladle. The second soldier on the left was charged with providing 50 bullets.[62] Prior to loading, the cannon would be well cleaned with a wet sponge to extinguish any smoldering material from the last shot. Fresh powder could be set off prematurely by lingering ignition sources. The powder was added, followed by wadding of paper or hay, and the ball was placed in and rammed down. After ramming the cannon would be aimed with the elevation set using a quadrant and a plummet. At 45 degrees, the ball had the utmost range: about ten times the gun's level range. Any angle above a horizontal line was called random-shot. Water was available to dip the sponges in and cool the pieces every ten or twelve rounds.[62]
Cannon in a Civil War re-enactment: The large amounts of gunpowder often affected visibility significantly. Gunners hope for a strong wind that will allow them to continue to see their target.
Britannica mentions "some occasions where 200 shots have been fired from these pieces in the space of nine hours, and 138 in the space of five."[62] During the Napoleonic Wars, a British gun team consisted of five gunners to aim it, clean the bore with a damp sponge to quench any remaining embers before a fresh charge was introduced, and another to load the gun with a bag of powder and then the projectile. The fourth gunner pressed his thumb on the vent hole, to prevent a draught that might fan a flame. The charge loaded, the fourth would prick the bagged charge through the vent hole, and filled the vent with powder. On command, the fifth gunner would fire the piece with a slowmatch.[63] In musicThe cannon has been used as a percussion instrument in certain pieces of music, one of the best known examples being Pyotr Ilyich Tchaikovsky's 1812 Overture.[64] The overture is properly played using an artillery section together with the orchestra, resulting in noise levels requiring musicians to wear ear protection.[65] It is supposed to simulate the Battle of Borodino, specifically, emperor Napoleon Bonaparte's retreat from Russia in 1812, and the rounds of cannon fire during the battle.[64][65] When the piece was first played, the cannon were fired by an electric current triggered by the conductor.[66] However, the piece was not recorded with actual cannon fire until Mercury Records and conductor Antal Dorati's 1958 recording of the Minnesota Orchestra.[67] Cannon fire is also frequently used annually in presentations of the 1812 on the American Independence Day, a tradition started by Arthur Fiedler of the Boston Pops in 1974.[68][65] The hard rock band AC/DC also used cannon in their song For Those About to Rock (We Salute You).[69] The album of the same name also featured a cannon on its cover.[70] In live shows, real cannon were used to perform the piece.[71][69] Due to their impracticalities, cannon are generally only used for grand, theatrical pieces, often with a military theme. In the case of the 1812, the cannon may be replaced with bass drum, timpani, or a synthesizer.[72][73][74] Other firearms may also be used instead of cannon, such as a shotgun firing blanks.[73] RestorationCannon recovered from the sea are often extensively damaged from exposure to salt water, because of this, electrolytic reduction treatment is required to forestall the process of corrosion.[75] The cannon is then washed in deionized water to remove the electrolyte, and is treated in tannic acid, which prevents further rust and gives the metal a bluish-black color.[76][77] After this process, cannon on display may be protected from oxygen and moisture by a wax sealant. A coat of polyurethane may also be painted over the wax sealant, to prevent the wax-coated cannon from attracting dust in outdoor displays.[77] Notes
References
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