Look at this picture. They almost look similar. That shows how it can be confusing to understand the difference between the Main battle tank and self-propelled guns.  

The self-propelled gun (right) with the tank (left).

The primary purpose of a modern main battle tank (MBT) is to destroy enemy AFVs (Armoured Fighting Vehicles; this includes other tanks, infantry fighting vehicles, and self-propelled artillery), but they can also be used against softer targets.

Meanwhile, a self-propelled gun (SPG) is typically used as an indirect fire weapon against soft targets, with a secondary function against fortifications and armor.

To do this, the self-propelled gun is typically shielded against small infantry weapons, heavy machine guns, and artillery pieces if it is ambushed by recon units or trapped in counterbattery fire.

Since its intended location is behind enemy lines, it lacks protection from anti-tank guns. The gun is a howitzer with an elevation of more than 45 degrees, typically based on a towed type.

However, it is possible to lower it to a horizontal position and employ it as a direct-fire weapon against adversaries that are approaching the gun’s position; it does not have the complex optics that a top-of-the-line tank possesses, such as night vision or laser range-finding.

What is the Difference Between Tanks and Self-Propelled Guns

The turrets and tracks of many SPGs give them a superficial resemblance to tanks; indeed, many SPGs are based on tank chassis. 

However, other SPGs move on wheels, and during World War II, there have been several SPGs that are open-topped or even unarmored.

Self-propelled gun turrets are broader and taller than tank turrets since they don’t have to provide a small target with a low silhouette. However, they still need space for heavier ammunition and a gun crew or autoloader.

Armor protects the main combat tank from the front and sides, and a high-velocity cannon fires specialized armor-piercing solid rounds.

Other shells, such as high explosives (HE), can also be fired. However, they travel at a slower rate than the armor-piercing penetrators.

A 120mm HE tank shell is comparable in size to a 120mm HE artillery shell. Nevertheless, due to the shallow trajectory, the terminal effects are concentrated in a smaller area, and these shells are often less explosive than a 120mm HE mortar bomb.

But the shells are better at breaking up than mortar bombs because their walls are thicker and more rigid. 

This means that tank and artillery shells have a smaller blast radius than mortars, but they have a larger kill zone because they create more and bigger pieces that travel farther than lighter and smaller ones from mortar.

The only exception is HEAT (High Explosive Anti-Tank) ammunition, which has less of a fragmentation effect and relies on a focused blast. Even though it is used instead of HE as a dual-purpose munition in tanks, it is not a very good anti-personnel weapon.

Consequently, for a given caliber of weapon, the blast power of conventional HE is greater for mortars, tank guns, and artillery. The opposite holds for their relative lethality (the radius within which 50% of personnel will be killed). 

Despite this, a single 120mm mortar shell killed 68 people and injured 144 others in an attack on a busy marketplace in Sarajevo in 1994.

Indirect fire In Tanks and Self-Propelled Guns

Nonetheless, indirect fire is typically a weapon of mass destruction. It functions by blanketing a target with effective interlocking radii, destroying targets with blasts from different angles, suppressing the enemy’s ability to act effectively, or even neutralizing heavy weapons and vehicles.

2S7M ‘Malka’ 203mm self-propelled artillery gun-
2S7M ‘Malka’ 203mm self-propelled artillery gun-min

suppression means forcing personnel to take cover and psychologically assaulting them; neutralization means killing personnel and destroying optics and other delicate components.

As a result, the higher the number of rounds that explode in the target region, the less deadly each bullet is. The infantry can now approach closer to a bombardment before it is lifted, allowing them to march onto the target as soon as the barrage is lifted.

Direct fire In Tanks and Self-Propelled Guns

However, to use direct fire, you must be able to see your target properly. Targeting individual targets with individual shells instead of flooding an area needs precise accuracy.

There are always exceptions to every rule. Recently, guided artillery munitions have made it possible for a specialized anti-armor or bunker-busting shell to hit a tank or fortification exactly where it needs to be. 

This eliminates the need for saturation fire on such hardened targets and fills the direct fire support role. During World War II, self-propelled artillery was frequently employed as “attack guns,” firing direct fire, particularly by the Germans and Soviets.

The assault gun provided attackers with a mobile cannon to target enemy resistance locations when commanders found them on the front lines.

A tank chassis served as the foundation for this vehicle, but instead of a turret, it had a stationary, armored superstructure. Designed to assist front-line soldiers by destroying fortifications in areas where anti-tank defenses were likely to be found, it featured robust frontal protection.

After 1941, the Germans began equipping their SturmGeschuetz (StuG) IIIs with dual-purpose 75 mm anti-tank guns to supplement the initially rare long-75mm armed Panzer IV tanks.

This was done because the Germans’ assault guns frequently encountered tanks or were called upon to attack them in the role of impromptu tank destroyers.

The chassis could support a heavier weapon than the tank variant because the turret wasn’t included. Tanks were no match for the StuGs during the more defensive engagements after 1943. 

Their low silhouettes made them ideal for ambush positions in the narrow land of the Normandy bocage, for instance. However, they were still operated by the artillery and manned by gunners rather than tankers.

Early Soviet employment of open-topped SPGs equipped with 76.2mm gun-howitzers served as mobile anti-tank and infantry support weapons. However, they quickly adopted a strategy of putting heavier guns (122mm and 152mm) in casemates, a la StuG design.

These weapons were not high-velocity anti-tank cannons but rather howitzers employed for troops’ direct fire support against buildings and bunkers. They depended on the explosive strength of their huge shells to cripple enemy tanks.

They were so lethal in this function that they earned the moniker “beast killers” or “big cat killers,” and they used it even against German heavy armor in the latter years of the war.


Smart munitions are just one of the numerous possibilities available to self-propelled guns nowadays. Fuses can be set to point detonation, airburst, or delay, and carrier rounds can release many payloads such as sub-munitions, sensors, smoke, leaflets, and more.

The tank gun is only good for direct fire, which gives them an advantage (although the latest developments by arms manufacturers like Rheinmetall introduce electronically timed fuzes to facilitate airburst and behind-cover effects for tank shells).