The Armstrong was a large rifled cannon invented by an Englishman, Sir William George Armstrong in 1854. It's most noticeable feature was the series of graduated coils over a lengthwise tube, causing it to look like a giant collapsible telescope pulled out in overlapping circles. Because exploding guns were a constant problem, and potentially devastating for the man who lie the charge as well as those around him, the Armstrong design was a huge success. The compressed inner tube in the cannon enabled it to better resist the force of firing. The cannon had four-inch and 16-pounder models. It was also manufactured in the United States using Armstrong's design. It was made in both muzzle-loading and breech-loading designs and came in sizes ranging from three to 13.3 inches. A three-inch muzzle-loading Armstrong could fire a grooved projectile, which weighed 12 pounds out to a distance of 2,000 meters. A three-inch breech-loading Armstrong fired a 12 pound projectile out to a distance of 2,000 meters. During the battle of “Dos de Mayo”, the Junin Tower, located at the northern defenses, used two 500-pound Armstrongs while the Merced Tower, at the southern ones, fired two revolving Armstrong guns. During that same battle, from a distance of 4,500 feet a 300-pound grenade from a Peruvian Armstrong hit the Numancia, piercing the protected ship from side to side.
English Captain Alexander Blakely invented the Blakely cannon. The most commonly used Blakelys had a bore of 3.1 to 10 inches and used a variety of ammunition, including flanged and studded projectiles. The 12-pounder Blakely was constructed of steel and iron had a bore of 3.4 inches and a tube that weighed 800 pounds. Using a one-pound charge, it fired a 10 pound projectile at a muzzle velocity of 1,250 ft/sec. The largest Blakely had a 12.75-inch bore and fired projectiles weighing 470 pounds nearly 2,000 yards (at 5 degrees of elevation). The large eight-inch Blakely was mainly for use in coastal defenses. As with its sister cannon, the Armstrong, the Blakely's rifled design helped absorb the impact of firing. However, because of its 'bucking back' when firing it did not remain as popular as the Armstrong and the Whitworth guns. When used with English ammunition, the Blakely was a good muzzle-loading gun, however, its performance deteriorated when firing shells of other manufacture In 1864, the Peruvian Government instructed its Consul in London, Mr. Enrique Kendall, to buy, among other weapons and ammunition, twelve pieces of artillery, all 11-inch Blakelys. The guns were sold trough two contracts that provided six pieces each. On April of that year a Peruvian military mission lead by artillery Colonel Francisco Bolognesi was sent to England to supervise the transaction and the quality of the armament. The guns arrived in Peru in early 1865. At “Dos de Mayo” eight heavy Blakelys were used. For example, at the northern defenses, Fort Ayacucho had two 450-pound Blakelys while the Railroad Battery had a 450- pound Blakely gun. Two more 450-pound blakelys were placed at the southern defenses (Fort Santa Rosa). During the war with Chile, some changes were made. The Santa Rosa fort kept her two 11-inch Blakelys. The Manco Capac and Independencia turrets had two 11-inch Blakelys each while Fort Ayacucho kept one 11-inch Blakely. The Blakely gun quickly became obsolete and soon was seeing little service as more advanced gun designs were produced.
The American Navy Commander John Dahlgren designed the Dahlgren. It was a large smooth bore cannon cast in the distinctive "soda bottle" shape. This design provided extra thick walls at the breech end of the gun which allowed for larger, heavier cannon that were less likely to explode at the breech when fired. Although originally designed to fire shells against wooden ships of the era, the Dahlgren cannons proved to be strong enough to fire 170-pound solid shot which was more effective even against ironclads. The 15-inch gun weighed over 20,000 pounds and required a hoist and a two-man crew to load the 400-pound spherical solid shot. The monitor Atahualpa and Manco Capac used two 15-inch Dahlgren guns during their encounters against the Chilean fleet. The defenses at the port during the war with Chile had two XV-inch Dahlgrens each at forts Pierola and Tarapaca. Also, along the harbor’s sea pier was a series of sandbagged batteries mounting five XV-inch Dahlgrens and two XI-inch Dahlgrens. Fort Ayacucho had one XV-inch Dahlgren and Fort Rimac had four XV-inch Dahlgrens.
The Rodman gun on the other side was a manufacturing process rather than a cannon, developed by Thomas Rodman in the mid-1840 for casting large iron cannon. The process made the guns stronger, longer lasting, and less likely to develop cracks. Rodman's process had the gun cast about a hollow pipe in which water was pumped during the cooling process while the outer part of the casting was kept hot by live coals. Rodman's process permitted larger guns to be manufactured than was previously possible. The 15-inch and 20-inch Rodman´s were the largest used. They were bottle shaped and weighed in at 25 tons. Rodman also improved the gunpowder used in the large guns. The 15-inch Rodman guns were capable of hurling a 440-pound shot more than four miles. These guns were used in coastal defenses and fortifications and were capable of firing a large shell or ball up to several miles and were excellent defensive weapons. They were not and never meant to be, mobile, often weighing in excess of 20 tons. Peru used a big 20-inch Rodman to protect Callao against the Chilean incursions.
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