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The trunnions are the protrusions from the side of the barrel that rest on the carriage. Belarus-Vitsebsk-Monument to Heroes of Patriotic War of 1812-6.jpg
The trunnions are the protrusions from the side of the barrel that rest on the carriage.

A trunnion (from Old French "trognon", trunk [1] ) is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development. [2]


Alternatively, a trunnion is a shaft that positions and supports a tilting plate. This is a misnomer, as in reality it is a cradle for the true trunnion. [ citation needed ]

In mechanical engineering (see the trunnion bearing section below), it is one part of a rotating joint where a shaft (the trunnion) is inserted into (and turns inside) a full or partial cylinder.

Medieval history

Early Chinese cannon with trunnions, Yuan Dynasty (1271-1368). Kept in Zhejiang Provincial Museum. Yuan Cannon (16918857248).jpg
Early Chinese cannon with trunnions, Yuan Dynasty (1271–1368). Kept in Zhejiang Provincial Museum.

In a cannon, the trunnions are two projections cast just forward of the center of mass of the cannon and fixed to a two-wheeled movable gun carriage. [3] As they allowed the muzzle to be raised and lowered easily, the integral casting of trunnions is seen by military historians as one of the most important advances in early field artillery.[ citation needed ]

16th-century depiction of a cannon with trunnions Renaissance Cannon 2.jpg
16th-century depiction of a cannon with trunnions

With the creation of larger and more powerful siege guns in the early 15th century, a new way of mounting them became necessary. Stouter gun carriages were created with reinforced wheels, axles, and “trails” which extended behind the gun. Guns were now as long as eight feet in length and they were capable of shooting iron projectiles weighing from twenty-five to fifty pounds. When discharged, these wrought iron balls were comparable in range and accuracy with stone-firing bombards. [4]

Trunnions were mounted near the center of mass to allow the barrel to be elevated to any desired angle, without having to dismount it from the carriage upon which it rested. Some guns had a second set of trunnions placed several feet back from the first pair, which could be used to allow for easier transportation. [5] The gun would recoil causing the carriage to move backwards several feet but men or a team of horses could put it back into firing position. It became easier to rapidly transport these large siege guns, maneuver them from transportation mode to firing position, and they could go wherever a team of men or horses could pull them. [6]

Initial significance

Due to its capabilities, the French- and Burgundy-designed siege gun, equipped with its trunnions, required little significant modification from around 1465 to the 1840s.

Gun trunnions often bear factory markings Museo de Artilleria de Cartagena-Canon de costa 150-45 1.jpg
Gun trunnions often bear factory markings

King Charles VIII and the French army used this new gun in the 1494 invasion of Italy. Although deemed masters of war and artillery at that time, Italians had not anticipated the innovations in French siege weaponry. Prior to this, field artillery guns were huge, large-caliber bombards: superguns that, along with enormous stones or other projectiles, were dragged from destination to destination. These behemoths could only be used effectively in sieges, and more often than not provided just a psychological effect on the battlefield; owning these giant mortars did not guarantee any army a victory. The French saw the limitations of these massive weapons and focused their efforts on improving their smaller and lighter guns, which used smaller, more manageable projectiles combined with larger amounts of gunpowder. Equipping them with trunnions was key for two reasons: teams of horses could now move these cannons fast enough to keep up with their armies, without having to stop and dismount them from their carriages to achieve the proper range before firing. Francesco Guicciardini, an Italian historian and statesman, sometimes referred to as the “Father of History,” wrote that the cannons were placed against town walls so quickly, spaced together so closely and shot so rapidly and with such force that the time for a significant amount of damage to be inflicted went from a matter of days (as with bombards) to a matter of hours. [4] For the first time in history, as seen in the 1512 battle of Ravenna and the 1515 Battle of Marignano, artillery weaponry played a very decisive part in the victory of the invading army over the city under siege. [7] Cities that had proudly withstood sieges for up to seven years fell swiftly with the advent of these new weapons.

Defensive tactics and fortifications had to be altered since these new weapons could be transported so speedily and aimed with much more accuracy at strategic locations. Two significant changes were the additions of a ditch and low, sloping ramparts of packed earth (glacis) that would surround the city and absorb the impact of the cannonballs, and the replacement of round watchtowers with angular bastions. These towers would be deemed trace Italienne. [8]

Whoever could afford these new weapons had the tactical advantage over their neighbors and smaller sovereignties, which could not incorporate them into their army. Smaller states, such as the principalities of Italy, began to conglomerate. Preexisting stronger entities, such as France or the Habsburg emperors, were able to expand their territories and maintain a tighter control over the land they already occupied. With the potential threat of their land and castles being seized, the nobility began to pay their taxes and more closely follow their ruler’s mandates. With siege guns mounted on trunnions, stronger and larger states were formed, but because of this, struggles between neighboring governments with consolidated power began to ensue and would continue to plague Europe for the next few centuries. [6]


In dams

A common floodgate used in dams and canal locks is the Tainter gate. This gate opens and closes by pivoting on a trunnion which extends into the mass of the dam or lock. The Tainter gate is used in water control dams and locks worldwide. The Upper Mississippi River basin alone has 321 Tainter gates, and the Columbia River basin has 195. [9]

In vehicles

In other technology

Trunnion bearings

In mechanical engineering, it is one part of a rotating joint where a shaft (the trunnion) is inserted into (and turns inside) a full or partial cylinder. Often used in opposing pairs, this joint allows tight tolerances and strength from a large surface contact area between the trunnion and the cylinder. [20]

In airframe engineering, these are self-contained concentric bearings that are designed to offer fluid movement in a critical area of the steering.

The term is also used to describe the wheel that a rotating cylinder runs on. For example, a lapidary (stone-polishing) cylinder runs on a pair of rollers, similar to trunnions. The sugar industry uses rotating cylinders up to 22 feet (7 m) in diameter, 131 ft (40 m) long, and weighing around 1,000 tons[ which? ]. These rotate at around 30 revolutions per hour. They are supported on a pathring, which runs on trunnions. Similar devices called rotary kilns are used in cement manufacturing.

In mining, some refining plants utilise drum scrubbers in the process that are supported by a large trunnion and associated trunnion bearings at each end.

See also

Related Research Articles

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Carronade Smooth-bore, short-barrel naval cannon

A carronade is a short, smoothbore, cast-iron cannon which was used by the Royal Navy. It was first produced by the Carron Company, an ironworks in Falkirk, Scotland, and was used from the mid-18th century to the mid-19th century. Its main function was to serve as a powerful, short-range, anti-ship and anti-crew weapon. The technology behind the carronade was greater dimensional precision, with the shot fitting more closely in the barrel thus transmitting more of the propellant charge's energy to the projectile, allowing a lighter gun using less gunpowder to be effective. Carronades were initially found to be very successful, but they eventually disappeared as naval artillery advanced, with the introduction of rifling and consequent change in the shape of the projectile, exploding shells replacing solid shot, and naval engagements being fought at longer ranges.

Rodman gun Type of American Civil War–era cannon

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Railway gun Form of large artillery

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Brooke rifle

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24 cm SK L/40 "Theodor Karl" Railroad gun

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38 cm SK L/45 "Max" Naval gun

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