Self-propelled gun

A self-propelled gun (SPG) is a gun, whether it be an artillery piece, anti-tank gun, or anti-aircraft gun, mounted on a motorized wheeled or tracked chassis. As such the gun can be maneuvered under its own power as opposed to a towed gun that relies upon a vehicle or other means to be moved on the battlefield. Self-propelled guns are combat support weapons; they are employed by combat support units fighting in support of, or attached to, the main combat units: infantry and armour.

It may be armoured, in which case it is considered an armoured fighting vehicle (AFV). Although the two are superficially similar self-propelled guns should not be confused with tanks. As a rule self-propelled guns are more lightly armoured and often lack turrets. Tanks are armed with guns designed specifically to destroy other tanks while only some types of self-propelled guns are designed for anti-tank warfare.

Some self-propelled guns are used as artillery pieces in a similar manner to traditional towed howitzers and as such also fall under the umbrella description of self-propelled artillery, but the two terms are not the same and the one is not a sub group or specialization of the other.

The greatest tactical advantage in the case of artillery guns is clearly the greater degree of mobility they have compared to towed artillery. Not only is it important in offering military forces greater flexibility, but it is critical in avoiding attack from the enemy (counter-battery fire) by allowing the guns to change position immediately after firing one or more salvos and before their position can be located ("shoot-and-scoot" tactics). A secondary advantage in the case of armoured – even lightly – guns is the increased protection offered to the gun crews.

Types

There are four broad types of self-propelled gun; some may be able to fulfill more than one role.

Artillery

Self-propelled artillery and howitzers are used in the same way as their towed variety, generally for long-range bombardment. Self-propelled artillery can however also include other types of weapons not considered a "self-propelled gun", one example of which would be rocket artillery.

Assault guns

Assault guns are large-caliber artillery pieces, meant to support infantry by direct fire with high explosive ammunition.

Anti-tank guns

Tank destroyers are self-propelled anti-tank guns with guns powerful enough to be effective against main battle tanks. They are often used in defence and withdrawal operations.

Anti-aircraft guns

These guns are designed to defend against attack by enemy aircraft, but they can also be used for direct fire against targets on the ground in close support of infantry.

Examples

*Self-propelled artillery:
**Gun Carrier Mark I, British WWI
**Birch gun, British Inter-war experiment
**M7 Priest, US, WWII
**G6 Howitzer, modern South African 155 mm howitzer
**M107 Self-Propelled Gun, US, modern
**PzH 2000, modern German 155 mm howitzter
**M109 howitzer, US modern
**SSPH Primus, modern 155 mm howitzer developed for the Singapore Armed Forces

*Assault gun:
**Sturmgeschütz III, German WWII
**SU-122, Soviet WWII
**ISU-152, Soviet WWII

*Anti tank gun:
**Deacon, UK WWII, truck-mounted gun
**SU-85, Soviet WWII
**SU-100, Soviet WWII
**M10 Tank Destroyer, US WWII
**M36, US WWII

*Anti-aircraft guns:
**Möbelwagen, German WWII
**ZSU-23-4, modern Soviet four barreled (23 mm) gun