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A gun turret is a weapon mount 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. The turret is also a rotating weapon platform. This platform can be mounted on a fortified building or structure such as an anti-naval land battery, or on a combat 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 general environment in which the weapon or its crew will be operating. The term comes from the pre-existing noun turret—a self-contained protective position which is situated on top of a fortification or defensive wall, as opposed to rising directly from the ground, when it constitutes a tower.
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.
The first naval vessel to be fitted with a turret was HMS Trusty of 1860, which was fitted with the prototype Coles turret. The first operational use was by USS Monitor of 1862, 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".
Early ships like Monitor and the converted HMS Royal Sovereign had little sea-keeping qualities being limited to coastal waters. HMS Captain of 1869 was one of the first sea-going turreted sailing ships. Poor design led to a top-heavy, low freeboard vessel and it was lost in a gale.
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.
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 World War II battleships where a heavily armoured enclosure protected the large gun crew during battle. The calibre of the main armament on large battleships was typically 30 to 46 centimetres (12 to 18 in) . The turrets carrying the 460 mm guns of Yamato each weighed around 2,500 tonnes. The secondary armament of battleships (or the primary armament of cruisers) was typically between 127 and 152 millimetres (5.0 and 6.0 in). Smaller ships typically mounted guns from 76 millimetres (3.0 in) upwards, although these rarely required a turret mounting.
In naval terms, 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 minute1
The loading system is fitted with a series of mechanical interlocks that 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.
A wing turret is a gun turret mounted along the side, or the wings, of a warship, off 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 HMS Dreadnought but not 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 at enemies to 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 muzzle blast.
Wing turrets were commonplace on capital ships and cruisers during the late 19th century 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 ship's 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 put 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 those in front of 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.
Many modern surface warships have mountings for large calibre guns, although the calibres are now generally between 3 and 5 inches (76 and 130 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.
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 in front of the bridge, and letters near the end of the alphabet (i.e., "X," "Y," etc.) for turrets behind the bridge ship—"Y" being the rearmost. Mountings in the middle of the ship would be "P," "Q," "R," etc. Confusingly, the Dido-class cruisers had a "Q" and the Nelson-class battleships 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.2
Exceptions were of course made; the battleship HMS Agincourt had the uniquely large number of seven turrets. These were numbered "1" to "7" but were unofficially nicknamed "Monday", "Tuesday", etc. through to "Sunday".
In German use, turrets were generally "A," "B," "C," "D," "E" going backwards from bow 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.
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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).
Turret of the Maginot Line; this could retract into the ground when not firing, for added protection
At first, guns on aircraft were either fixed in orientation or mounted on pedestals or 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, as in the "lobsterback" rear seat of the Hawker Demon biplane fighter.
The first bomber in the Royal Air Force to carry an enclosed power-operated turret was the Boulton & Paul Overstrand twin-engined biplane, which first flew in 1933. The Overstrand, due to its speed, needed a completely enclosed front gun position and so was fitted with a turret - armed with one Lewis machine gun - at the front of the bomber. Movement of the gun on its mount actuated motors that rotated the turret.3 The American Martin B-10 all-metal monocoque monoplane bomber introduced turret-mounted defensive armament within the United States Army Air Corps, almost simultaneously with the RAF's Overstrand biplane bomber design. The Martin XB-10 prototype aircraft first featured the nose turret in June 1932, and was first produced as the YB-10 service test version by November 1933. The production B-10B version started service with the USAAC in July 1935.
In time the number of turrets carried and the number of guns mounted increased. RAF heavy bombers of World War II typically had three powered turrets, with the rear one—the tail gunner or "Tail End Charlie" position—mounting the heaviest armament of four 0.303 inch Browning machine guns or, late in the war, two AN/M2 light-barrel versions of the American Browning M2 machine gun.
During the World War II era, British turrets were largely self-contained units, manufactured by Boulton Paul Aircraft and Nash & Thomson. The same model of turret might be fitted to several different aircraft types. Some models included gun-laying radar that could lead the target and compensate for bullet drop.
The UK introduced the concept of the "turret fighter", with aeroplanes such as the Boulton Paul Defiant where the armament (four 0.303 inch) 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 thought 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 impaired the airplane's speed and maneuverability relative to a conventional fighter which the flexibility of the turret armament could not compensate for. At the same time conventional fighter designs were flying with 8 or more machine guns. Attempts to put heavier armament (multiple 20 mm cannon) in low profile aerodynamic turrets were explored by the British but were not successful.
Not all turret designs put the gunner in the turret along with the armament. Both the Americans and Germans produced aircraft with remote controlled turrets. In the US, the large, purpose-built Northrop P-61 Black Widow night fighter was produced with a remotely-operated dorsal turret that had a wide range of fire though in practice it was generally fired directly forward under control of the pilot. For the last production blocks of the B-17F, and for all versions of the B-17G Flying Fortress a twin-gun remotely operated "chin" turret, designed by Bendix and first used on the experimental YB-40 "gunship" version of the Fortress, was added to give more forward defence. Specifically designed to be compact and not obstruct the bombardier, it was operated by a swing-away diagonal column possessing a yoke to traverse the turret, and aimed by a reflector sight mounted in the windscreen.
The intended replacement for the German Bf 110 heavy fighter, the Messerschmitt Me 210, possessed twin half-teardrop-shaped, remotely-operated Ferngerichtete Drehringseitenlafette FDSL 131/1B turrets, one on each side "flank" of the rear fuselage to defend the rear of the aircraft, controlled from the rear area of the cockpit. By 1942, the German He 177A Greif heavy bomber would feature a Fernbedienbare Drehlafette FDL 131Z remotely operated forward dorsal turret, armed with twin 13mm MG 131 machine guns on the top of the fuselage, which was operated from a hemispherical, clear rotating "astrodome" just behind the cockpit glazing and offset to starboard atop the fuselage — a second, manned powered HDL 131 dorsal turret, further aft on the fuselage with a single MG 131 was also used on most examples. The US B-29 Superfortress had four remote controlled turrets, comprising two dorsal and two ventral turrets. These were controlled from a trio of gunner-manned sighting stations operated from the pressurised sections in the nose and middle of the aircraft, in addition to a B-17 style flexible manned tail gunner's station.
The defensive turret on bombers fell from favour with the realization that bombers could not attempt heavily defended targets without escort regardless of their defensive armament unless very high loss rates were acceptable, and the performance penalty from the weight and drag of turrets reduced speed, range and payload and increased the number of crew required. The British de Havilland Mosquito light bomber was designed without any defensive armament and used its speed to avoid engagement with fighters, much as the minimally-armed German Schnellbomber aircraft concepts had been meant to do early in World War II.
A small number of aircraft continued to use turrets however—in particular maritime patrol aircraft such as the Avro Shackleton used one as an offensive weapon against small unarmoured surface targets. The Boeing B-52 jet bomber and many of its contemporaries (particularly Russian) featured a tail-mounted barbette (a term from British English), or "remote turret" —an unmanned turret but often with more limited field of fire.
Aircraft carry their turrets in various locations:
- "dorsal" – on top of the fuselage, sometimes referred to as a mid-upper turret.
- "ventral" – underneath the fuselage, often on American WW II heavy bombers, a Sperry-designed ball turret.
- "rear" or "tail" – at the very end of the fuselage.
- "nose" – at the front of the fuselage.
- "cheek" - on the flanks of the nose, as single-gun flexible defensive mounts for B-17 and B-24 heavy bombers
- "chin" – below the nose of the aircraft as on later versions of the Boeing B-17 Flying Fortress.
- "wing" – a handful of very large aircraft, such as the Messerschmitt Me 323 and the Blohm & Voss BV 222, had manned turrets in the wings
- "beam" (British English) or "waist" (American English) – mounted on the sides of the rear fuselage eg American twin- and four-engined bombers.
Consolidated B-24 Liberator nose turret
The Bendix-designed B-17 chin turret
A preserved North American B-25 Mitchell, showing the dorsal turret
B-29 remote controlled ventral turret
Avro Lancaster tail turret
Various early armoured cars such as the Lanchester and Rolls-Royce Armoured Cars of 1914 were fitted with turrets, but the first tracked combat vehicles did not have them, and it was not until late in World War I that the French Renault FT-17 light tank introduced the single fully rotating turret carrying the vehicle's main armament that continues to be the standard of almost every modern main battle tank and many self-propelled guns.
In the 1930s, several nations produced multi-turreted tanks—probably influenced by the British Vickers A1E1 Independent of 1926. Those that saw combat during the early part of World War II performed poorly and the concept was soon dropped. Combat vehicles without turrets, with the main armament mounted in the hull, or more often in an integral armored casemate as part of the main hull, saw extensive use by German and Russian forces during World War II as Tank destroyers and assault guns. However, post-war, the concept fell out of favour due to its limitations, with the Swedish Stridsvagn 103 'S-Tank' and the German Kanonenjagdpanzer being exceptions.
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. Machine guns may be mounted inside the turret, which on modern tanks is often on a "coaxial" mount, parallel with the larger main cannon. On modern tanks, the turret houses all the crew except the driver (who is located in the hull). The crew located in the turret typically consist of tank commander, gunner, and often a gun loader (except in tanks that utilize an automated loading mechanism).
For other combat 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.
The size of the turret is a factor in combat vehicle design. One dimension mentioned in terms of turret design is "turret ring diameter" which is the size of the aperture in the top of the chassis into which the turret is seated.
- Capt. S. W. Roskill, RN, HMS Warspite, Classics of Naval Literature, Naval Institute Press, 1997 ISBN 1-55750-719-8
- The Nelson design was an adaption of an earlier planned battleship with two turrets before the bridge and a single one behind the bridge but in front of the aft superstructure.
- The Overstrand's Turret Flight 1936
- Air Gunnery November 1943 Popular Science article on aircraft turrets
- Flight article on aircraft gun turrets amongst others
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