An AS90 Self-Propelled Gun in Salisbury Plain
Weapons and Kit

Know Your Armoured Vehicles - Self-Propelled Artillery Versus Tanks

An AS90 Self-Propelled Gun in Salisbury Plain

To the untrained eye, there may seem to be similarities in the look of self-propelled artillery (SPA) and tanks - and indeed there are, but both have been developed for specific roles on the battlefield.

The uninformed could be forgiven for confusing the two - both are armoured vehicles on tank tracks, and both have large guns.

Another way to describe it might be to say that SPA has either large guns, or howitzers (which are essentially guns that fire at a higher trajectory, allowing for indirect fire.)

Since howitzers are not always technically classed as artillery, SPA is sometimes referred to more comprehensively as SPGs (self-propelled guns), and they can in fact also carry other weapons like mortars and rockets.

The use of and potential roles for SPA are also varied, and complex, though the basic difference with a tank is that SPA is meant to be mobile artillery.

Like a field gun that is positioned somewhere on the battlefield (often behind frontline troops), its job is to support infantry or other units.

The key is it is more mobile than a field gun, which needs to be towed. SPA can drive itself to where it is needed and fire from there. Or it can continue driving itself to keep up with other armoured vehicles and units that it is intended to support.

British Army SA90 SPA shown on the move and firing

Tanks, on the other hand, usually go into battle directly rather than supporting a battle indirectly. They have turrets that allow for easy rotation of their guns, which fire at a flatter trajectory more suited for direct fire upon their intended targets.

Tanks also have thicker armour, making them more suited to this direct combat role.

As is often the case with technology, there are, of course, exceptions - such as the Jagdtiger pictured below – since supporting other units sometimes exposes SPGs/SPA to considerable fire, such as when they serve in an anti-tank role.

One common feature that sets self-propelled artillery apart, though, is that instead of turrets, they often have gun casemates, which are essentially like the kind of fortified gun emplacements regular artillery guns are shielded behind. The difference and key of SPA casemates though is that, like the guns, they are hauled around on tracks.

And because SPA uses casemates rather than turrets, they usually do not have the same ability to swivel their guns from side to side easily, like a tank does.

German Jagdtiger 1 tank destroyer self-propelled gun
Notice the casemate on the top of this German Jagdtiger 1 tank destroyer, an exception in the SPG arena due its having thick armour (image: Mark Pellegrini)

Stuart Wheeler, Archive and Library Manager at the Tank Museum in Bovington, has set out some key differences between SPAs and tanks and some of the history that led to the development of the two forms of firepower.

How To Distinguish Between Self-Propelled Artillery (SPA) And A Tank

To the uninformed, an SPA can look a little like a tank, so what makes them different?

Mr Wheeler points out that, while there are always exceptions (such as the Swedish S-Tank), the trick is identifying what makes and SPA 'not a tank'.

For instance, if it has a turret, is the turret open topped, that is, without a roof? Does it have a visible gun shield? Is the gun clearly identifiable as a large howitzer with the capability for high elevation?

If the turret superstructure is fixed then it may be more likely to be a tank destroyer, which is explained later, or SPA platform than a tank.

Swedish S-Tank
A Swedish S-Tank, a tank with no turret (image:Jorchr)

Why Were SPA And Tanks Both Developed?

If tanks are basically mobile gun platforms designed to support infantry, and SPA are mobile gun platforms designed to support infantry, at least originally, why did we manufacture both?

Mr Wheeler suggested that the first tanks to reach the battlefield on September 15th, 1916, were only armed with 6-pounder (57mm) guns.

The tanks were designed to crush barbwire, cross trenches and support the infantry with sustained machine-gun and 6-pounder fire, but they were essentially direct assault platforms only, and they were at their most formidable in combined-arms-warfare actions.

What SPA allowed was for larger-calibre artillery pieces to maintain indirect fire support by increasing their mobility and thus their range, freeing support weapons from the need to be towed into position.

What Are The Key Roles Of SPA Over Tanks?

SPA usually has larger-calibre guns than a tank, yet it is more lightly armoured, and there can be advantages of SPA over tanks in battle situations.

Mr Wheeler said that, basically, SPA are not expected to be fighting directly against other AFVs (Armoured Fighting Vehicles) – which a key difference with a tank (unless an SPG is serving in an anti-tank role.)

The job of SPA is to provide support fire from long range. This (usually) indirect support role means they do not typically have the same thickness of armour as a tank, They are fitted with enough armour to protect them from small arms and shell splinters, however.

Also, even though they are often in an indirect support role, the whole point of SPA is that their mobility allows them to keep up with armoured formations, rather than slowing them down, as towed artillery might do.

A Challenger 2 tank (image: MoD)
A Challenger 2 tank (image: MoD)
An AS90 self-propelled gun (image: MoD)
An AS90 self-propelled gun (image: MoD)

History Of Supporting Firepower

There are perhaps historical precursors to SPA, such as the “flying artillery” that gave the Americans such an advantage at the Battle of Palo Alto during the Mexican-American War.

But are there other historical forerunners for SPA, such as the British Gun Carrier Mark I?

Mr Wheeler said that it could be argued that fast mobile horse artillery, such as the Royal Horse Artillery, have offered commanders in the field direct and indirect supporting firepower from the 18th Century onwards.

However, he said it is the combination of mobility, increased range and limited armour protection that the 60-pounder gun on the Gun Carrier Mark I brought to the battlefield, not unlike the increased mobility of the SPA that would succeed it.

Tank Destroyers And Supporting Artillery

Mr Wheeler explained how there are both tank destroyers as well as supporting artillery in the SPA field.

Tank destroyers offer a generally cheaper, less well-armoured mobile anti-tank gun platform which can have the firepower of a tank but not its armour. Tank destroyers have been historically better used in defensive and ambush engagements.   

Challenger 3 seen in Germany
A Challenger 3 tank in Germany (image: MoD)

Tank Museum SPA

Visitors to the Tank Museum at Bovington are able to see examples of self-propelled artillery on display, with a particular focus on tank destroyer forms of SPA.

Examples include the Valentine Archer, an example of a WW2 UOR, and the M10 17-pounder, the Sturmguschütz ausf G, Jagdpanther and Jagdtiger. 

Cover image: A British Army SA90 hiding under camouflage netting (image: MoD)

Inside an AS90 SPG of the Royal Horse Artillery
Inside an AS90 SPG of the Royal Horse Artillery (image: MoD)