Gun laying: Wikis

  

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Gun laying is the process of aiming an artillery piece, such as a gun, howitzer or mortar on land or at sea against surface or air targets. In may be laying for direct fire, where the gun is aimed similarly to a rifle, or indirect fire where firing data is calculated and applied to the sights. The term includes automated aiming using, for example, radar-derived target data and computer-controlled guns.

Gun laying means moving the axis of the bore (of the barrel) in two planes, horizontal and vertical. A gun is traversed—rotated in a horizontal plane—to align it with the target; and elevated—moved in the vertical plane—to range it to the target.

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Description

The elevation angle uses 'data' derived from trials or empirical experience. For any given gun and projectile types, it reflects the distance to the target and the size of the propelling charge. It also incorporates any differences in height between gun and target. With indirect fire it may allow for other variables as well.

With direct fire the horizontal angle is usually the line of sight to the target, although the layer may make allowance for the wind and with rifled guns the sights may compensate for projectile 'drift'. With indirect fire the angle is relative to something, typically the gun's aiming point, although with modern electronic sights it may be a north seeking gyro.

Depending on the gun mounting, there is usually a choice of two trajectories. The dividing angle between these trajectories is about 45 degrees, it varies slightly due to gun dependent factors. Below 45 degrees the trajectory is called 'low angle'(or lower register), above is 'high angle' (or upper register). The differences are that low angle fire has a shorter time of flight, a lower vertex and flatter angle of descent.

Early guns could only be traversed by moving their entire carriage or mounting and this lasted with heavy artillery into World War 2. Mountings could be fitted into traversing turrets on ships, coast defences or tanks.

Recoil systems were invented in the late 19th Century and integrated into the gun carriage or mounting, usually in a cradle which had the trunnions and carried the barrel. They were a step-change in gun design and had a significant impact on gun laying arrangements.

Before their invention guns moved substantially backwards when they fired and had to be rolled forward before they could be layed. This meant that there was no great benefit in traversing the gun without moving the carriage. However, mortars, where the recoil forces were transferred directly into the ground (or water if they were on ships), did not always require such movement. Recoil system, which prevented guns moving backwards, led to the development of traverse mechanisms built into the carriage or mounting.

All guns have carriages or mountings that support the barrel assembly (called the ordnance in some countries). Before the late 19th Century a barrel usually had trunnions that fitted into the upper part of the carriage or mounting. This allowed the barrel to be moved in the vertical plane. Recoil systems were usually fitted in a cradle that held the barrel and the tunnions transfered from the barrel to the cradle.

However, with the adoption of recoil systems for field artllery it became normal to pivot the saddle on the lower carriage, initially this 'top traverse' was only a few degrees but soon offered a full circle, particularly for anti-aircraft guns.

In some gun mountings it is also possible to depress the gun, that is to move it in the vertical plane to point it below the horizontal, to fire down at a target. Such a facility is only relevant if the gun is higher than its target, though in some muzzle loading guns, the gun had to be depressed to load it.

An essential capability for any elevation mechanism is to prevent the weight of the barrel forcing its heavier end downwards. This is greatly helped by having trunnions at the centre of gravity, although other mechansms can be used. However, it also means that the elevations gear is strong enough that it can resist considerable downwards pressure but still be easy for the gun layer to use.

Muzzle Loading Artillery

A gun mounted on its carriage, with the gun tackle in place.

In the days of cannon, guns were provided with trunnions that were mounted onto a gun carriage. The gunner and gun-crew levered the front or rear of the carriage to traverse the gun from side to side, and drove in or pulled out wedges under the breech to achieve elevation. When fired the whole cannon on its carriage rolled backward against the resistance of a block and tackle rig. The recoil pushed the gun back far enough for the crew to access the muzzle to reload it, and when loaded the same block and tackle was used to return the carriage to its firing point. In the early 17th century certain castles and fortifications were fitted with gunloops or artillery ports to allow cannon to be fired from within. Often there was limited angle variation due to the confined gun port size, due to the masonry design to protect castle defenders.

On sailing warships in normal operation the guns were lashed down to the gun decks in the recoiled position, and the gun ports closed. To "run out the guns" was to open the gun ports, and haul the cannon forward to the firing position, a very threatening gesture, more so if the guns were actually loaded since blackpowder charges in the guns degenerate swiftly, and unloading a cannon without firing it is a dangerous process.

Breech Loading Artillery

A British 60-pounder (5 inch) gun at full recoil, in action during the Battle of Gallipoli, 1915.

Field artillery pieces where the gun is mounted on a wheeled gun carriage usually have a gun trail, by which it is towed, and this is manhandled to traverse the gun, although modern artillery provides for the ability to make fine adjustments to lateral aiming without traversing the entire carriage. Gun elevation is commonly set by a screw mechanism, and the gun mounting provides at least some range of depression, to allow direct fire from a height. There is usually a mechanism to absorb the majority of the recoil built into the gun carriage so the gun bucks when fired, but does not need to be winched back into place after firing.

Some of the first examples of breech loading artillery found limited use during the American Civil War, however it was not until the end of the 19th century that it began to supersede older muzzle loading cannons. The effectiveness of quick firing breech loading artillery that did not have to be re-laid after every firing was proven during the trench warfare of the First World War.

Naval Advances

USS Iowa fires a broadside

The first turreted warship to see service, the USS Monitor, revolutionized warfare at sea through the ability to bring all of its guns to bear without turning the ship. Naval guns mounted in batteries in gun turrets brought gun laying to a new level of sophistication.

In World War II era ships, turret traverse, gun elevation and recoil are managed using hydraulic power. Ballistic calculations are performed by analog computers called rangekeepers. The guns are fired electrically and a fire control system is arranged to fire the guns in sequence, firing each gun as the roll of the ship brings the gun to bear on its target.

Calculations of shell trajectory for the directing of artillery were one of the earliest tasks to which digital computers were applied. Naval gun laying was one of the earliest tasks to which servomechanisms and selsyns were applied; these would later be important to numerical control of machine tools. Thus the delivery of explosives to targets via artillery was a good example of military applications spurring the funding of technological development that would later have widespread civilian applications.


Modern Artillery and Aiming Systems

Current fighting vehicles have automated gun laying systems. In addition to the traditional ballistic calculations, these systems add additional aiming data to compensate for air temperature, wind direction, movement of the vehicle, and wear and straightness of the gun barrel. In the 1960s advanced military technology began to track targets using real time radar and other electronic intercept techniques. Gradually these systems developed into real-time computer controlled targeting and firing systems to allow optimisation of gun laying for ships, tanks, and ground-based artillery.

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