The cavalry were originally soldiers who traveled and fought on horseback, usually with swords or lances. There were two main types of cavalry:
- Light cavalry, lightly armed soldiers on small fast horses, which was responsible for seeking out and harassing the enemy; and
- Heavy cavalry, more heavily armoured soldiers, often wearing armour, on larger and more powerful horses.
Heavy cavalry were used as "shock" troops to attack infantry formations and other cavalry.
Although not strictly cavalry, the Australian Light Horse units of the First World War can be loosely classified as such. They used horses to move quickly and were organised in the same way as cavalry units, but actually did their fighting dismounted as infantry soldiers. Although some light horse units were issued with swords late in the war, their main weapon was the rifle and bayonet. With the mobility provided by their horses, they were well suited to the reconnaissance roles for which light cavalry had traditionally been used.
A mounted soldier, however, provided an easy target for a machine gun, and could be stopped by mud, barbed wire and trenches. The cavalry's usefulness on the battlefield was brought to an end by the industrialised slaughter of the Western Front. The horse was replaced with the tank. Its armoured protection rendered it impervious to the machine gun, and caterpillar tracks gave it the mobility on this new battlefield that the cavalry had once possessed. After the First World War cavalry units began converting to armoured units with tanks and armoured cars, but they carried with them still the dashing ethos and traditions of the cavalry. The first Australian Light Horse units began converting to armoured units during the 1930s and this process continued into the Second World War.
The role of armour on the battlefield is much the same as that of the old cavalry. Light armoured units in small armoured vehicles or tanks are responsible for reconnaissance while larger, more heavily armoured vehicles are used in the "shock" role, to attack enemy armour or to provide the infantry with mobile fire support.
Cavalry soldiers, and Australian light horsemen in particular, are known as "troopers". During the First World War light horsemen were nicknamed "Billjims", but now, having long ago traded in their horses for armoured vehicles, they are more commonly known as "turretheads".