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 and/or pivoting point. First associated with cannon, 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.

Trunnion positions saw table and provides a pivot point.

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

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.

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 had to be specially designed. Stouter gun carriages were created with reinforced wheels, axles, and “trails” which extended behind the gun. Guns would be up to eight feet in length and shoot iron projectiles weighing from twenty-five to fifty pounds. These wrought iron balls when discharged 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

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 such changes were the additions of a ditch and low, sloping ramparts of packed earth that would surround the city and absorb the impact of the cannonballs (glacis), 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 tighter control. With the 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 firearms

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.[21]

Philadelphia Penrose bridge c. 1880 (shown open) swings on a Trunnion Bearing.

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. 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


  1. "trunnion – definition of trunnion by the Free Online Dictionary, Thesaurus and Encyclopedia". Retrieved 2010-08-23.
  2. Keegan, John (1994). A History of Warfare. Vintage. ISBN 978-0-679-73082-8
  3. Duffy, Chris (1979) Siege Warfare: The Fortress in the Early Modern World 1494-1660. Routledge & Kegan Paul. ISBN 0-415-14649-6
  4. 1 2 Duffy, Chris (1979). Siege Warfare: The Fortress in the Early Modern World 1494–1660. Routledge & Kegan Paul. ISBN 0-415-14649-6
  5. Manucy, Albert (2008) Artillery Through the Ages. BiblioBazaar. ISBN 0-554-39597-5
  6. 1 2 McNeill, William H. (1982) The Pursuit of Power. University of Chicago Press. ISBN 0-226-56158-5
  7. Cipolla, Carlo M. (1965) Guns and Sails in the Early Phase of European Expansion 1400–1700. Collins Clear-Type Press, London. ISBN 0-308-60014-2
  8. Benedict, Phillip; Gutmann, Myran (2005) Early Modern Europe: From Crisis to Stability. Rosemont Publishing and Printing Corp. ISBN 0-87413-906-6
  9. Society of Automotive Engineers (1915). SAE transactions, Volume 10, Part 1. p. 180. Retrieved 22 April 2013.
  10. Piggott, Bill; Clay, Simon (2003). Original Triumph TR4/4A/5/6: The Restorer's Guide. MotorBooks International. ISBN 978-0-7603-1738-9. Retrieved 22 April 2013.
  11. Piggott, Bill; Clay, Simon (2009). Collector's Originality Guide Triumph TR2 TR3 TR4 TR5 TR6 TR7 TR8. MBI Publishing. p. 108. ISBN 978-0-7603-3576-5. Retrieved 22 April 2013.
  12. Schultz, Morton J. (June 1965). "To lube or not to lube". Popular Mechanics. 123 (6): 162–167. Retrieved 22 April 2013.
  13. "American Motors". Car Life. 10: 57. 1963. Retrieved 22 April 2013.
  14. Lombardo, David A. (1993). Advanced Aircraft Systems. McGraw–Hill. p. 266. ISBN 978-0-07-038603-7.
  15. Currey, Norman S. (1988). Aircraft landing gear design: principles and practices. American Institute of Aeronautics & Astronautics. pp. 175–177. ISBN 978-0-930403-41-6. Retrieved 22 April 2013.
  16. "Trucking terms Glossary". Volkema Thomas Miller & Scott. Retrieved 22 April 2013.
  17. "Spring Beam". Watson and Chalin. Retrieved 22 April 2013.
  18. Operator's, Organizational, Direct Support, and General Support Maintenance Manual for Compressor, Rotary, Air, DED, 250 CFM, 100 Psi Trailer-mounted. Department of the Army Technical Manual. 1990. pp. 150–151. Retrieved 22 April 2013.
  19. according to a web page at "www dot vacpartswarehouse dot com" [see next footnote] that was found using "a simple Google search for "trunnion cover"".
  20. "Hoover Cover Trunnion U5395 / Manufacturer's Part Number: 36131094". Archived from the original on April 10, 2015.
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