Copyright 2006 T. Sheil & A. Sheil All Rights Reserved
The idea of mobile artillery was put to use in the Civil War. Guns and mortars were mounted on railway cars. The advent of railway artillery was a major step in the development of fast-moving artillery. Railway guns were the main form of mobile artillery right into the First World War. The problem was their restriction to railway lines.
The overwhelming majority of artillery pieces were towed. In World War I, almost all was horse-drawn. The guns were adequate to keep up with the infantry and cavalry forces of the time. Experiments were made in mounting howitzers of tractors, but they were a novelty. Nonetheless, mechanization inspired some work in the direction of fast-moving artillery.
The development of the armored army concept by Heinz Guderian set a new requirement for all arms. Those included within the armored force had to be equally mobile with the tanks. They had to keep pace with the armored thrust, as theorized by Guderian. To this end came the idea of self-propelled guns. Rather than have them towed by a prime mover, the idea was to mount them on vehicles. These would be designed to work with tanks, keeping pace and affording some armored protection, themselves.
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The first need of any assault force was artillery support. German forces handled this in two ways. One was to mount conventional artillery onto the chassis of armored vehicles. Unlike tanks, these were installed open-topped compartments to give crews the room to work. Since conventional artillery works from behind the forward edge of battle, armor was light. Guns such as the Wespe (Wasp), a 105mm gun on a Panzer II chassis, gave German forces a mobile artillery that could keep pace with the tanks. In a pinch, they could also be used in a direct-fire role.
Field artillery provides indirect fire support. Using coordinates passed on by a forward observer, the artillery unit’s “fire direction control” calculates the angle of guns and the amount of powder needed to drop a shell on target. It is not the impact or velocity, but the explosion of the shell itself, that does the damage. The big guns are concerned with getting the shell on target.
Self-propelled guns make this mobile. Traditional towed guns must first be pulled into position ,and then set up by crews. That means positioning by hand, opening trains, digging in spades, etc. It takes time to get a gun emplaced to fire. With self-propelled guns, the gun is already emplaced on the chassis. The work is mostly a matter of getting the gun into place. While the unit must still set up its aiming stakes and aiming circle, it is freed from the task of unhooking and manhandling the gun.
A self-propelled gun can go where a tank can go.
Though they can do direct fire in a pinch, the self-propelled field gun is ill suited for use as a tank or tank destroyer. Its gun requires more work to fire, hence more crewmen. Its armor is very light, and man of these weapons’ fighting compartments are just barely bulletproof.
The second way of providing artillery was the close support tank. This was the Panzer 4. It was developed to carry a 75mm howitzer for use against infantry positions, anti-tank guns and similar targets. At the time the Panzer 4’s role was first engineered, the main guns of most tanks were 37mm to 45mm. They were good for antitank and anti-vehicular work. For firing high explosive, which is the role of artillery, they were poor weapons. Their small shells had less explosive power than a hand grenade. At best a 37mm to 50mm gun firing high explosive was a long range grenade launcher.
Close howitzer support was given over to a special tank. The Panzer 4 was supposed to serve solely as close artillery support, taking on objectives that required high explosive.
The United States was the master of artillery, much to the chagrin of the enemy. The American self-propelled guns were lightly-armored superstructures built on Lee or Sherman chassis. The M7 “Priest” 105mm guns and M12 155mm guns gave American forces a reliable mobile artillery. Britain developed the Sexton, a 25 pounder on M3 chassis. Soviet forces used the SU76, a light tank chassis with a 76mm gun in an open compartment.
For direct assault against enemy positions, the Germans developed their assault guns. Whereas tanks were slated for mobile combat, in the tradition of cavalry, the assault gun was a mobile artillery fortress for attacking fixed positions. Panzer 4s provided close support for tanks, and assault guns did the same for infantry.
The German assault gun was simple. Using a standard tank chassis of the time, they built a low, fortified superstructure around a howitzer. The Panzer III was the main battle tank of German forces from the 1930s to early 1943, and so provided the basis for the early assault guns. The superstructure was like a “pillbox” fortification instead of a turret. The gun had limited traverse. That was not a problem, since the idea was to point the vehicle at a stationary target and move toward it while attacking it with the howitzer. The assault gun was a form of siege artillery, and so it was considered an artillery weapon rather than tank.
The
Sturmgeschutz (Storm Gun) became the standard assault gun for German forces, and
would remain so for much of the war. It was originally seen in the early Stug 3
version with 75mm howitzer., the number denoting the Panzer III chassis on which
it was built.
Keep in mind that the assault gun formula was developed when a tank’s main gun was 37mm to 50mm. Tank guns could not be used effectively in any artillery role. Effective dual-purpose guns (antitank and high explosive) would emerge with the long-barreled 75mm gun.
Later upgrades to the Stug 3 were a 75mm long barreld, dual purpose gun. A “Sturmhaubitze” (Storm Howitzer) with a long 105 mm howitzer was the final version of the III. Several Stug IV versions emerged from 1943 to 1945. These carried a 75mm dual-purpose gun, and functioned as tank destroyers rather than assault guns.
American assault
guns were unlike their German counterparts. The American tanks were more in the
line of close support vehicles. The M4A3E8 Sherman with 105mm gun and 75mm gun
carriage on Stuart light tank chassis were called “assault guns.” The Americans
did not charge a position, but stood off and shelled it.
Britain’s assault guns were , like the Americans, a close support weapon. Engineering tanks for hitting fortifications were fitted with spigot mortars.
Soviet forces used assault guns, the first being the KVII with its immense turret and 152mm gun. Turretless guns includes the SU85 and SU100, using the T34 chassis and mounting 85mm and 100mm guns, respectively. The heavy guns were the SU 122 and SU 152, mounted on JS / KV chassis. These were used in the assault gun mode.
Part and parcel of Guderian’s armored theory was the support of anti-tank guns. The guns themselves were mounted on wheeled carriages, to be towed by trucks. A mobile anti-tank gun was the product of an obsolete tank and a powerful gun. The Germans took the potent Czech 47mm gun and fitted it into an open-topped supersctructure. This was built on the Panzer 1, a vehicle already obsolete by the invasion of Poland. In effect, the German had succeeded in making the anti-tank gun as mobile as the tanks it supported. After the invasion of France, German mounted heavy guns on the Panzer II and Czech 38T chassis. These were collectively known as “Marders”. They all featured a lightly-armored, open topped superstructure on a light tank chassis
The mobile anti-tank gun was taken a step further with the Tank Destroyer concept. The German version of the tank destroyer was a mobile anti-tank gun in a well-armored housing. The German tank destroyers used the assault gun structure: a boxlike armored fortress on a tank chassis, housing a gun in a limited-traverse housing. They were used to provide support to tanks, acting as anti-tank guns The German tank destroyers could double as assault guns. Their great weaknesses were limited traverse and lighter armor on sides and rear.
American Tank Destroyers had lighter armor than tanks. The M10, M36 and M18 Hellcat had open-topped, traversing turrets mounting the 3 inch / 76mm, 90mm and 76mm guns, respectively. Another tank destroyer involved placing a 75mm gun on a half track. The turretless vehicle was not used by the United States.
Britain made the Archer, a turretless anti-tank gun that used a Valentine chassis. The gun faced backward, the theory being that it made for a faster get-away.
The Soviets used the SU85 and SU 100 as tank destroyers.