Self-propelled artillery entered the stage as early as 1917 CE, with the appearance of the British Gun Carrier Mark I.
It consisted of the heavily modified carriage of the Mark I tank with a 60-pounder gun mounted on top.
Despite its innovation it was never used in action, employed only briefly as a transport.
After World War I most artillery remained horse-drawn.
Some was pulled by trucks or tractors, but these were relatively rare because both the vehicles and their fuel were expensive.
Generally light trucks handled light and medium artillery; tractors heavy.
The heaviest guns of all could not be carried on road vehicles so were mounted on train carriages instead: the railway guns.
The picture changed during the course of World War II.
Blitzkrieg tactics, pioneered by the Germans and soon adopted by most parties involved,
required fast moving artillery that could keep pace with tanks and motorized infantry.
More and more artillery guns were transported by trucks.
Targeting methods improved to be able to cope with moving, rather than static, targets.
Radio was used to communicate between gunners and forward observers; airplanes complemented the latter.
In battles of maneuver even that was not enough.
Artillery had to be able to rapidly drive up to the right position, fire and race away to avoid counter-fire: 'shoot-and-scoot'.
Therefore the artillery guns were mounted onto the vehicles, rather than trundled after them.
Some vehicles retained normal wheels, while others adopted tank tracks to be able to deal with rough terrain.
In order to shield the crew, the new self-propelled artillery pieces were also armored, though never as thoroughly as tanks.
Modern heavy self-propelled artillery has a caliber of about 150 - 155 millimeters, fires 5 - 10 rounds per minute up to 30 kilometers away and is lightly armored.
Some shoot conventional rounds; others fire rockets.
War Matrix - Self-propelled artillery
World Wars 1914 CE - 1945 CE, Weapons and technology