Why do Tanks use Angled Armor? - Tank Historia

Why do Tanks use Angled Armor?

Armored vehicles come in all shapes and sizes, but, as indicated by the name, they all aim to provide protection against enemy weapons. This can be done in many different ways, with bulletproof glass, simple steel plates or more complex composite armor.

Angled armor – also known as sloped armor – is another method employed by designers to improve a vehicle’s durability. Since WWII this technique has been used on a wide scale and it can be identified easily: is the armor positioned up right, or at an angle?

Its simple to spot angled armor, but what advantages does it actually provide? When is it used? And why isn’t it always employed?



Armor is one of the key components of any armored fighting vehicle (AFV). It is one piece of the “holy trinity” of tank design: armor, firepower and mobility.

Any tank will have a specific blend of these three qualities. Too much of one can negatively impact another, while too little can compromise the function of the vehicle. There are many more factors involved in a tank’s design, but these three are a general rule of thumb in the making of a successful design.

Abrams in the Desert.
The Abrams is an excellent example of a vehicle that balances the “holy trinity”. It possesses great speed, armor and a potent gun.

The idea of armor protection did not start with tanks, as it has been employed for centuries in various forms on ships, defensive structures and worn by soldiers. It can consist of steel plates, steel castings, composite armor and reactive armor. More recently, tanks have come equipped with active protection systems that attempt to destroy incoming projectiles before they even reach the armor.

The first tanks introduced in WWI were protected by riveted steel plates. Militaries quickly adapted to this new threat by firing large caliber or high velocity weapons at them. Soon, dedicated anti-tank guns made dealing with their armor easier.

A Mark V heavy tank.
WWI era vehicles are rather primitive by todays standards, but even with just 16 mm of armor, this was more than enough to handle most weapons it faced.

By WWII armor was welded together and becoming increasingly thick to hold up against new, powerful anti-tank weapons.

It was around this time that angled (also known as sloped) armor saw use on an appreciable scale.

Once again, this idea was not new, but it wasn’t until WWII that angled armor it really took off.

Angled Armor

The concept of angled armor is rather simple: it is armor that is at any angle other than vertical or horizontal.

The main goals of angled armor is to increase the chances of deflecting or deforming an incoming round and to more efficiently protect a vehicle.

Additionally, angled armor can increase the effective thickness of a given plate (assuming a projectile travels along a horizonal path).

Angled Armor diagram 1
Regardless of a plate’s angle, effective thickness is generally measured from a line of sight trajectory (horizontal).

To put it simply: by angling a piece of armor, a projectile has to penetrate more material.

For example, to penetrate a 100 mm thick vertical plate, a projectile travelling along a flat trajectory would have to pierce through 100 mm.

If this exact same plate was angled 45 degrees from vertical, the projectile would have to pierce 141 mm.

The new thickness that must be defeated by a projectile is known as the “effective thickness”.

Angled Armor Diagram 2
As shown here, simply angling a plate backwards by 45 degrees significantly increases its effective thickness.

The effective thickness of the plate increases significantly as the angle decreases. A plate angled at 20 degrees from vertical has an effective thickness increase of about 7 percent, while angling a plate at 40 degrees increases its effective thickness by around 30 percent.

This means a thinner plate positioned at an angle can have the same effective armor as a thicker, vertically mounted one. This logic is often used to explain that angled armor reduces a vehicle’s weight as you can use thinner, and therefore lighter plates.

However this is not always the case. When a plate is angled, its height is reduced. As a result, a thin, angled plate must be larger than a vertical one, negating any savings in weight.

Angled Armor Diagram 3
Simply angling a plate does not work, as the angle decreases the plate’s vertical height. As shown in this diagram, an angled plate needs to be larger (indicated by the lined areas). This can actually increase a tank’s weight.

Advantages of Angled Armor

So if angled armor doesn’t provide much in the way of weight savings, why would anyone use it?

Angled armor has a number of advantages over more basic armor layouts.

First of these is manufacture. Flat armor must be thicker to provide adequate protection, but thick armor plates are hard to produce.

To make good quality armor, the steel’s grain and internal structure must be carefully controlled. This is fairly simple to do with thin plates, but it gets progressively harder to control as the steel increases in thickness.

As we’ve discussed, angled plates can be thinner without loosing effective thickness. Therefore, designers can opt for thinner plates that are easy to manufacture yet don’t comprise protection.

Angled Armor Diagram 6
When mounted at 60 degrees, the plate on the left becomes effectively as thick as the plate on the right. This means designers can use thinner, easy-to-make plates instead of thick ones and still have the same level of protection.

One of the biggest motives behind using angled armor is how incoming rounds interact with it. To penetrate armor, a projectile would ideally hit it straight on, allowing it to concentrate its energy in a small area on the thinnest possible amount of armor.

There are many, many factors at play when a projectile hits a piece of angled armor, but in general it greatly decreases the chances of a successful penetration (at least when hit by conventional, solid shot rounds).

When hitting sloped plates, a projectile is forced to deviate from its original trajectory, dispersing its energy over a greater area which can be better absorbed by the armor.

Angled Armor Diagram 5
Angled armor can cause a round to deviate from its original path, increasing the area its energy is distributed across. A round that can hit a plate square on is able to focus its energy in a smaller area.

Alternatively the round may ricochet off the armor.

In other scenarios, a projectile can be bent against the angled metal, changing their shape and can even cause them to simply shatter. Angled armor is most effective against short and relatively light projectiles.

These results were particularly common with WWII era ammunition, as anti-tank rounds were often short and relatively light.

While angled armor offers little protection against shaped charge projectiles, it can increase the chances of these rounds failing to operate properly.

A simple WWII round.
WWII ammunition was relatively simple compared to modern standards. Shown is an M72 armor piercing round used by the Sherman.


As with anything, angled armor comes with a few disadvantages. Most prevalent of these is a tank’s interior space when fitted with this armor configuration – or more accurately, the lack of interior space.

Angling armor may increase protection, but it significantly reduces the space inside the tank needed for the crew and equipment. Tanks like the T-34 were pioneers for their use of angled armor, but in return they were extremely cramped inside.

T-34 armor.
The T-34 is famous for its extensive use of angled armor. However, it came at a cost.

To solve this, many designers simply opted to used angled armor where it was needed most – the front. The Sherman is notable for this, with a highly angled front and vertical sides.

The Germans are often accused of not realising the benefits of angled armor until later in the war, particularly with the Tiger, but this was not actually the case. They were fully aware of this layout, but opted to go with a thick, flat sided tank to improve interior conditions.

After WWII, long-rod penetrators became increasingly popular and much more developed. Angled armor was rendered mostly useless by these long, dense and extremely high velocity projectiles.

Long rod penetrator sabot seperating.
Long-rod pentrators are extremely powerful, and are a match for the very toughest armor on the battlefield.

Their great length allows them to negate angled armor, as they bend in such away that aligns them with the armor’s actual thickness.

Additionally, a bent and deformed long-rod penetrator can behave in ways similar to a much larger caliber round, causing even more devastation.

However armor at extreme angles (around 75 degrees or more) can cause long-rod penetrators to ricochet.

Angled Armor Diagram 4
Angled armor can deflect some types of ammunitions, but it is less effective against long-rod penetrators, which have a tendency to “bend in” towards the armor’s actual thickness.

Surprisingly, flat armor is actually better suited to stopping these sorts of rounds.

The introduction of composite armor also removed the need for angled armor. As this type of armor is designed to shatter incoming rounds with its physical properties and extreme volume, it tends to be mounted in large, flat sections on modern vehicles.

Another Article From Us: Why are Some Tanks Covered in Blocks?

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Despite this, armor angling can still be found on active vehicles all around the world. It is useful for less potent munitions, and is a cheap, effective way of improving armor protection.