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Aug. 06, 2024

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Oscillating turret - Wikipedia

Two-part gun turret with elevation hinge

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An oscillating turret is a form of turret for armoured fighting vehicles, both tanks and armoured cars. The turret is unusual in being made of two hinged parts. Elevation of the gun relies on the upper part of the turret moving relative to the lower part.

Oscillating turrets have rarely been used. Their only widespread use was on two French designs: the AMX-13 light tank and the Panhard EBR armoured car; the Austrian SK-105 Kürassier uses a turret developed from the AMX-13.[1]

Design

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SK-105 Kürassier, showing the low height of the turret above the gun barrel

The turret consists of upper and lower parts, joined by a trunnion. The gap between these two parts is often covered by a visible rubber or canvas bellows.

The gun itself is fixed to the upper part of the turret. Elevation of the gun is achieved by tilting the entire upper part of the turret. In conventional designs, the gun is mounted inside the one-piece turret by a trunnion, and its elevation is changed by tilting on that trunnion while the turret remains in fixed position relative to the hull. Traverse in both designs is achieved by rotating the turret.

In oscillating turrets where the oscillating part of the turret is enclosed gives the advantage that the gunner and loader always is in line with the gun allowing easier aiming and loading.

Pros & Cons

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SK-105 Kürassier 19 ton light tank of the Bolivian Army with 105mm gun in oscillating turret,

There are three primary advantages: higher placement of the gun in the turret, smaller turret size, and easier fitment of an autoloader.

In a conventional design, the clearance between the breech of the gun and the ceiling inside the turret determines how far the gun can be depressed. In an oscillating design, the gun and the upper part of the turret move as a unit, so no extra room is needed. The gun can therefore be mounted at the top of the turret, which may allow the turret to be smaller and lighter. The design may also increase the maximum angle of depression.

Additionally, in a conventional design elevating the barrel of the gun pivots the breech into the tank hull, which requires the turret ring to be large enough to allow this. In an oscillating design, the breech may remain above the turret ring, in which case the ring can be smaller, potentially allowing the hull to be smaller as well.

Note, however, that the maximum gun elevation angle with an oscillating turret is determined by the clearance between the rear of the turret and the deck of the hull. This may result in lower maximum elevation and range than that possible in a conventional design. For this reason, oscillating designs often have the gun mounted higher above the deck. An oscillating turret's overall height is likely to be similar to that of a conventional design, but with the gun mounted higher within the turret. The lower hull position relative to the gun may allow better protection in the hull-down position.

Another advantage is that, since the breech is fixed relative to the upper turret, it may be easier to fit an autoloader. Doing so would enable decreasing the vehicle's crew by one and decreasing the volume of the turret.

One disadvantage of the oscillating turret design is that the turret and its armor is split into two pieces. This is necessarily weaker than a one-piece design, and so is less optimal for main battle tanks and other large armored vehicles. On top of that the gap between upper and lower parts of the turret is rather hard to seal which results in problem with protection from elements, fording and making the vehicle NBC proof.

Compact turrets

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Heavy tanks and the AMX-50

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AMX-50 with 120 mm Tourelle D

The initial claimed advantage of oscillating turrets was that of reducing the turret size for a large main battle tank gun. In the s, tanks were rapidly growing more heavily armed, larger and heavier. Western armed forces were trying to catch up with the increasingly formidable Soviet tanks, such as the T-55. Weight was the main problem, particularly where this then required extra engine power and stronger transmission. As the thickest armour is generally on the turret, reducing turret size appeared to be a worthwhile goal.

Size may be reduced because the non-elevating gun breech does not need to move up and down inside the upper turret. Working space thus does not need to be allowed for it above or below the breech, space that is normally wasted in conventional turret designs. In particular, the oscillating turret design is particularly shallow above the breech, allowing for a low turret silhouette, a considerable advantage.

This was the justification for the first oscillating turret, that of the French AMX-50 medium or heavy tank in the 50 tonnes class. This used first a 90 mm, then 100 mm, gun in an oscillating turret, primarily to save weight. The final 120 mm version first reverted to a conventional turret, but then used another oscillating design, the Tourelle D. However the need to elevate the gun still requires room for the breech to be lowered into the lower turret. This has tended to produce oscillating turret designs with a high gun axis relative to a conventional turret, even where the turret height is otherwise shallow.

One problem was that the armour of a turret is primarily in the front face of the turret and this was not made any smaller in the AMX-50 design, the turret of the 120 mm version being so tall as to be reminiscent of the WW2 Challenger, the turret being a whole foot taller than the contemporary and comparably armoured Conqueror. The AMX-50 grew progressively heavier and although it might have proved a capable heavy tank by s standards, this whole class of slow-moving AFV was becoming outdated by the development of lightweight anti-tank guided missiles in the s and so the project was abandoned.

Light tanks

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Whilst the oscillating turret was unsuccessful for the heavy tank, it proved more successful in allowing light tanks and armored cars to carry an unusually heavy main gun of 90 mm. In French doctrine, light reconnaissance vehicles were heavily armed and expected to also fulfill a role in defending the flanks of a main force. They were not expected to act as tank destroyers though, and so a high-caliber but relatively low velocity gun with high-explosive shells was effective in their role.

As the gun remains fixed relative to the upper turret, it is easier to install an autoloader than for a conventional turret, where the gun must return to a fixed elevation for reloading. The French design used two six-round rotating magazines, allowing a high rate of fire and also a selection of two ammunition types. The disadvantage was that once the magazine ready capacity was used, reloading of the magazines was a slow process requiring the vehicle to rest and crew to operate outside the vehicle, which could not be carried out under fire.

As was so often the case with the early autoloaders though, their complexity was their downfall. The 120mm for the AMX-50 was simply unreliable, due to the weight of the ammunition round.

AFVs fitted with oscillating turrets

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French

Austrian

SK-105 Kürassier &#; Used the 105 mm FL-12 turret of the AMX-13[3]

German

Kugelblitz &#; Mounted dual 30mm MK 103 cannon in a novel oscillating ball mount.
Begleitpanzer 57 AIFSV &#; 57 mm gun mounted in an external cradle on the turret.

Egyptian

Sweden

United States

Argentina

Patagón &#; Light tank, prototypes only

South Korea

North Korea

M Mobile Gun System copy

References

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If you are looking for more details, kindly visit turret rotation mechanism.

Further reading

Lau, Peter (). The AMX-13 Light Tank. Vol. 2: Turret. Rock Publications.

Oscillating Turrets - How They Work -

Oscillating turrets are a unique type of turret that can be found on some armored fighting vehicles. They differ from conventional tank turrets in a number of ways, most notably in how they look and move, plus their natural acceptance of autoloading mechanisms.

For a brief period &#; mainly in the s and s &#; oscillating turrets experienced an explosion in popularity.

Designers looking for new great breakthroughs explored this type of turret as they provided a number of useful benefits.

Many countries experimented with oscillating turrets in the s. This tank is an American T54E1, armed with a 105 mm autoloading gun in an oscillating turret.

Most oscillating turret-armed tanks did not make it past the prototype stage though, as for the most part they do not offer enough advantages over conventional turrets to use them on a large scale.

There are a few exceptions to this however, like the AMX-13.

Continue reading to discover the good, the bad and the ugly of oscillating turrets.

What is an Oscillating Turret?

An oscillating turret is a turret that uses two separate parts to achieve rotation and elevation.

Conventional turrets are a single rotating unit that contains the main gun and crew. In this arrangement, the gun is moved left and right by rotating the entire turret, and moves up and down by pivoting the gun up or down inside the turret.

Oscillating turrets separate the turret into two &#; with one piece controlling elevation and the other controlling rotation.

These two parts are simply referred to as the &#;upper&#; and &#;lower&#; parts. The lower part is also sometimes called the &#;collar&#;.

The main components of an oscillating turret.

The upper part contains the gun, and the two move up and down together as a single, fixed piece.

The lower part rotates the entire assembly like a conventional turret.

The upper part is attached to the lower part via trunnion, allowing it to pivot.

The upper piece of the oscillating turret, which contains the gun, pivots up and down as a single piece.

The French intensely experimented with this type of turret in the s and were the first to bring a tank into active service with such a turret.

This was a fascinating era for tank designs, as the end of WWII and the beginning of the Cold War saw tanks become increasingly powerful and heavily armored.

The AMX-50 project used a number of different oscillating turrets. In the end it was too complex, too expensive and an engine couldn&#;t be sourced.

Designers were looking for anything that could give them an edge over the enemy, and the oscillating turret was one of the many technologies investigated. One of the first tanks to carry its gun in an oscillating turret was the AMX-50.

Advantages

The main motivation for using an oscillating turret is size, as they are usually more compact than conventional turrets and allow for a smaller hull. But they also offer a number of other benefits.

Inside a normal turret, there must be sufficient room above the breech of the gun to stop it hitting the roof when depressed. This requires a higher, and therefore heavier turret.

Gun depression in a normal turret is limited by the breech hitting the turret roof, as shown here. Oscillating turrets do not suffer from this.

Any time the gun isn&#;t depressed this is simply wasted room.

With an an oscillating turret, the turret itself moves up and down with the gun, negating any need for extra room above the breech.

This difference means the gun can be mounted higher up in the turret, reducing the turret&#;s size and weight.

In combat a high mounted gun is extremely useful as it can make the turret a smaller target. As less &#;forehead&#; above the gun is exposed when cresting a hill, the enemy has to hit a much smaller target.

Both of these turrets contain a similar 120 mm gun, but the AMX-50 is a significantly smaller target thanks to its higher mounted gun in the oscillating turret.

Furthermore, gun depression with an oscillating turret is only limited by the barrel touching the hull of the tank, rather than the breech touching the turret roof.

This is similar for gun elevation too. In a normal turret, when a gun is elevated its breech will lower into the hull of the tank. The turret ring must be large enough to allow for this.

As the upper turret section of an oscillating turret is mounted above the top of the hull, the breech doesn&#;t need to depress into the hull when elevated.

Tanks with these turrets can carry larger guns and yet have smaller turret rings. A smaller turret ring means a smaller and lighter hull.

Finally, oscillating turrets are ideal for autoloaders. One of the biggest challenges of fitting an autoloader is ensuring the breech of the gun is lined up with the loading mechanism.

Tanks with conventional turrets will either have the autoloader follow the breech&#;s movement to keep in line with the gun, or automatically move the gun into a suitable position between shoots to facilitate a smooth entry for the next round.

Many tanks that use oscillating turrets, including the proposed Kranvagn, use an autoloader.

Oscillating turrets make this much simpler as the gun is fixed to the turret. In this arrangement, the autoloading mechanism is permanently lined up with the breech and can load shells in at any angle.

This further helps to reduce the turret&#;s size, as an autoloading gun no longer needs the internal space for a human loader.

Despite these excellent traits, oscillating turrets come with a few inherent drawbacks that are virtually impossible to solve.

Disadvantages

The two parts of an oscillating turret are naturally weaker than a single piece design, potentially making them an inferior choice for heavy tanks that are meant to taking a beating.

And although they can allow the gun to elevate without passing through the turret ring, elevation can be limited by the rear of the upper turret striking the hull deck.

But arguably the most significant drawback of an oscillating turret is the difficulty in sealing it for nuclear, biological and chemical (NBC) systems.

Most tanks with oscillating turrets will have some sort of canvas or rubber seal where the two turret halves meet. Image by FaceMePLS CC BY 2.0.

The gap between the two moving parts is usually covered by a rubber or canvas seal, but this is not as secure as a conventional turret. In an age where tactical nuclear weapons were a real threat, this was simply not good enough for many militaries.

In conclusion, these types of turrets are excellent at carrying a large gun on a small tank, and that&#;s one of the main reasons they have been employed.

The French have the most experience with these turrets. They discovered that the autoloaders for very large guns in heavy tanks suffered from poor reliability due to the size of the shells.

The mighty AMX-50 Surbaissé.

They did however see great success with smaller tanks armed with comparatively large guns.

Another Article From Us: AMX-50 Surbaissé &#; A Mighty French Autoloader

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Other countries who experimented with oscillating turrets found that they didn&#;t offer significant enough advantages to justify switching over from normal designs.

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