Gun turret

A gun turret is a device that protects the crew or mechanism of a projectile firing weapon and at the same time lets the weapon be aimed and fired in many directions.

A turret is a rotating weapon platform. This can be mounted on a fortified building or structure such as an anti-naval land battery, or on an armoured fighting vehicle, a naval ship, or a military aircraft.

Turrets may be armed with one or more machine guns, automatic cannons, large-calibre guns, or missile launchers. It may be manned or remotely controlled, and is often armoured. A small turret, or sub-turret on a larger one, is called a cupola. The term "cupola" also describes rotating turrets that carry no weapons but instead sighting devices, as in the case of tank commanders. A finial is an extremely small sub-turret or sub-sub-turret mounted on a cupola turret.

The protection provided by the turret may be against battle damage or against the weather, conditions and environment in which the weapon or its crew operate.

The term comes from turret - a protective position on a fortification situated on top of a building or wall, as opposed to rising directly from the ground which is a tower.

Warships

History

[
BL 15 inch /42 naval gun; compare the layout and nomenclature with the American design below.]

Before the development of large-calibre, long-range guns in the mid-19th century, the classic battleship design used rows of port-mounted guns on each side of the ship, often mounted in casemates. Firepower was provided by a large number of guns which could only be aimed in a limited arc from one side of the ship. Due to instability, fewer larger and heavier guns can be carried on a ship. Also, the casemates often sat near the waterline, which made them vulnerable to flooding and restricted their use to calm seas. Turrets allowed the smaller number of guns to be aimed and fired on both sides of the ship and at the same time provided armoured protection to the gun crew.

One of the earliest turret gun ships was the USS "Monitor", which mounted two muzzle loading cannons in a fully rotating armoured drum. An alternative at the time used a static drum, the barbette, inside which the gun mount rotated - the gun barrel projecting over the edge of the drum. In latter designs this was developed to have an armoured portion that sat over the gun and the edge of the barbette, leading to the term "hooded barbette".

With the advent of the South Carolina class battleships in 1908, main battery turrets were designed so as to superfire, to improve fire arcs on centerline mounted weapons. This was necessitated by a need to move all main battery turrets to the vessel's centerline for improved structural support. This is a stark contrast to the contemporary HMS "Dreadnought" which, while revolutionary in many other ways, still retained wing turrets. The superfiring or superimposed arrangement had not been proven until after "South Carolina" went to sea, and it was initially feared that the weakness of the previous Virginia class ship's stacked turrets would repeat itself.

Another major advancement was in the Kongō class battlecruisers and Queen Elizabeth class battleships, which dispensed with the "Q" turret amidships in favour of heavier guns in fewer mountings.

While World War I ships commonly had a twin-turret configuration, ships by World War II were commonly using triple and even quadruple turrets, which reduced the total number of mountings altogether and improved armour protection, though quad mount turrets proved to be extremely complex to arrange, making them unwieldy in practice.

The largest warship turrets were in WWII battleships where a heavily armoured enclosure protected the large gun crew during battle. The calibre of the main armament on large battleships was typically 12 in (30 cm) up to 18 in (45 cm). The turrets carrying the 18-inch guns of "Yamato" each weighed around 2,500 tons(?). The secondary armament of battleships (or the primary armament of cruisers) was typically between 5 and 6 in (127 - 152 mm). Smaller ships typically mounted guns from 3 in (76 mm) upwards, although these rarely require a turret mounting.

Layout

In naval terms, a turret traditionally and specifically refers to a gun mounting where the entire mass rotates as one, and has a trunk that pierces the deck. The rotating part of a turret seen above deck is the gunhouse, which protects the mechanism and crew, and is where the guns are loaded. The gunhouse is supported on a bed of rotating rollers, and is not physically attached to the ship; were the ship to capsize, the turret would fall out. Below the gunhouse there may be a working chamber, where ammunition is handled, and the main trunk, which accommodates the shell and propellant hoists that bring ammunition up from the magazines below. There may be a combined hoist ("cf" the animated British turret) or separate hoists ("cf" the American turret cutaway). The working chamber and trunk rotate with the gunhouse, and sit inside a protective armoured barbette. The barbette extends down to the main armoured deck (red in the animation). At the base of the turret sit handing rooms, where shell and propelling charges are passed from the shell room and magazine to the hoists.

The handling equipment and hoists are complex arrangements of machinery that transport the shells and charges from the magazine into the base of the turret. Bearing in mind that shells can weigh around a ton, the hoists have to be powerful and rapid; a 15 inch turret of the type in the animation was expected to perform a complete loading and firing cycle in a minute [Capt. S. W. Roskill, RN, "HMS Warspite", Classics of Naval Literature, Naval Institute Press, 1997 ISBN 1-55750-719-8] The loading system is fitted with a series of mechanical interlocks that (in theory) ensure that there is never an open path from the gunhouse to the magazine down which an explosive flash might pass. Flash-tight doors and scuttles open and close to allow the passage between areas of the turret. Generally, with large-calibre guns, powered or assisted ramming is required to force the heavy shell and charge into the breech. As the hoist and breech must be aligned for ramming to occur, there is generally a restricted range of elevations at which the guns can be loaded; the guns return to the loading elevation, are loaded, then return to the target elevation. The animation illustrates a turret where the rammer is fixed to the cradle that carries the guns, allowing loading to occur across a wider range of elevations.

Earlier turrets differed significantly in their operating principles. It was not until the last of the "rotating drum" designs described in the previous section were phased out that the "hooded barbette" arrangement above became the defining turret.

Wing turrets

A wing turret is a gun turret mounted along the side, or the wings, of a warship, off of the centerline.

The positioning of a wing turret limits its arc of fire, so that it generally can contribute to only the broadside weight of fire on one side of the ship. This is the major weakness of wing turrets as broadsides were the most prevalent type of gunnery duels. Depending on the configurations of ships, such as the HMS "Dreadnought" but not the SMS "Blücher", the wing turrets could fire fore and aft, so this somewhat reduced the danger of crossing the T and the turrets could fire to enemies at the rear.

Attempts were made to mount wing turrets "en echelon" so that they could fire on either beam, such as the Invincible and SMS "Von der Tann" battlecruisers, but this tended to cause great damage to the ships deck from the gun blast.

Wing turrets were commonplace on capital ships and cruisers during the late 1800s up until the early 1910s. In pre-dreadnought battleships, the wing turret contributed to the secondary battery of sub-calibre weapons. In large armoured cruisers, wing turrets contributed to the main battery, although the casemate mounting was more common. At the time, large numbers of smaller calibre guns contributing to the broadside were thought to be of great value in demolishing a ships upperworks and secondary armaments, as distances of battle were limited by fire control and weapon performance.

In the early 1900s, weapon performance, armour quality and vessel speeds generally increased along with the distances of engagement; the utility of large secondary batteries reducing as a consequence. Therefore, the early dreadnought battleships featured "all big gun" armaments of 11 or 12 inches calibre, some of which were mounted in wing turrets. This arrangement was not satisfactory, however, as the wing turrets not only had a reduced fire arc for broadsides, but also because the weight of the guns was putting great strain on the hull and it was increasingly difficult to properly armour them.

Larger and later dreadnought battleships carried superimposed or superfiring turrets (i.e one turret mounted higher than, and firing over, that in front and below it). This allowed all turrets to train on either beam, and increased the weight of fire forward and aft. The superfiring or superimposed arrangement had not been proven until after "South Carolina" went to sea, and it was initially feared that the weakness of the previous Virginia class ship's stacked turrets would repeat itself. Larger and later guns (such as the US Navy's ultimate big gun design, the 16"/50 Mark 7) also could not be shipped in wing turrets, as the strain on the hull would have been too great.

Modern turrets

Many modern surface warships have mountings for large calibre guns, although the calibres are now generally between 3 and 5 inches (76-127 mm). The gunhouses are often just weatherproof covers for the gun mounting equipment and are made of light un-armoured materials such as glass-reinforced plastic. Modern turrets are often automatic in their operation, with no humans working inside them and only a small team passing fixed ammunition into the feed system. Smaller calibre weapons often operate on the autocannon principle, and indeed may not even be turrets at all, they may just be bolted directly to the deck.

Naming

On board warships, each turret is given an identification. In the British Royal Navy, these would be letters: "A" and "B" were for the turrets from the front of the ship backwards, and letters near the end of the alphabet (i.e., "X," "Y," etc.) for turrets in the rear of the ship. Mountings in the middle of the ship would be "P," "Q," "R," etc. Confusingly, the Dido class had a "Q" and the Nelson class had an "X" turret in what would logically be "C" position; the latter being mounted at the main deck level in front of the bridge and behind the "B" turret, thus having restricted training fore and aft.

Secondary turrets were named "P" and "S" (Port and Starboard) and numbered from fore to aft, e.g. "P1" being the forward port turret.

Exceptions were of course made; the battleship HMS "Agincourt" had an unusually large number of seven turrets. These were named "Monday", "Tuesday", etc. up to "Sunday".

In German use, turrets were generally "A," "B," "C," "D," "E" going backwards from stem to stern. Usually the radio alphabet was used on naming the turrets, e.g. "Anton", "Bruno" or "Berta", "Caesar," "Dora" as on the German battleship "Bismarck".

Land fortifications

Gun turrets have been placed in static, land fortifications such as the Maginot Line forts in France and particularly in coastal artillery defences such as Fort Drum, the "concrete battleship", near Corregidor, Philippines. Some nations, from Albania to Switzerland and Austria, have embedded the turrets of obsolete tanks in concrete fortifications (usually to secure choke points such as mountain passes).

Aircraft

At first, guns on aircraft were either fixed in orientation or mounted on simple swivel mounts. The latter evolved into the Scarff ring, a rotating ring mount which allowed the gun to be turned to any direction with the gunner remaining directly behind it. As aircraft flew higher and faster, the need for protection from the elements led to the enclosure or shielding of the gun positions. The first bomber in the Royal Air Force to carry a power operated turret was the Boulton Paul Overstrand which first flew in 1933. The Overstrand had a single turret, which was at the front of the bomber fitted with one machine gun. In time the number of turrets carried and the number of guns mounted increased. RAF heavy bombers of the Second World War typically had three powered turrets, with the rear one - the Tail gunner or "Tail End Charlie" position - mounting four 0.303 inch machine guns

The Martin B-10 introduced turret-mounted defensive armament within the United States Army Air Corps, nearly a year ahead of the Overstrand, with a power-operated nose turret.

The UK introduced the concept of the "turret fighter", likely based on the World War I success of the two-seater Bristol F.2 Fighter against the single-seat fighters of two decades earlier, in planes such as the Boulton Paul Defiant where the sole armament (4 x 0.303 in (7.7 mm) machineguns) was in a turret mounted behind the pilot rather than in fixed positions in the wings. The concept came at a time when the standard armament of a fighter was only two machine guns. In the face of heavily armed bombers operating in formation it was felt that a group of turret fighters would be able to concentrate their fire flexibly on the bombers; making beam, astern and from below attacks practicable. Although the idea had some merits in attacking bombers, it was found to be impractical when dealing with other fighters; the weight and drag of the turret slowed the aeroplane relative to a fixed armament single seater. The defensive turret on bombers fell from favour with the advent of the jet age, though the Boeing B-52 jet bomber and many of its contemporaries featured a tail-mounted barbette, or "remote turret" - a form of turret but with more limited field of fire. However like other turrets these were soon phased out to reduce manpower needs as well as to increase payload and speed.

Aircraft carry their turrets in various locations:

*"dorsal" - on top of the fuselage
*"ventral" - underneath the fuselage
*"rear" or “tail” - at the very end of the fuselage
*"nose" - at the front of the fuselage
*"chin" - below the nose of the aircraft

Armoured fighting vehicles

In modern tanks the turret is armoured for crew protection and rotates a full 360 degrees carrying a single large-calibre tank gun, typically in the range of 105 mm to 125 mm calibre. Aiming machine guns may be mounted inside the turret. The turret houses two or more crewmen, typically a tank commander, gunner, and often a gun loader.

For other armoured fighting vehicles, the turrets are equipped with other weapons dependent on role. An infantry fighting vehicle may carry a smaller calibre gun or an autocannon, or an anti-tank missile launcher, or a combination of weapons. A modern self-propelled gun mounts a large artillery gun but less armour. Lighter vehicles may carry a one-man turret with a single machine gun.

ee also

*Sponson
*Barbette

References