After Heavy Horse Archers become Dragoons, they gain +15 hit points, +2 attack strength, +1 line of sight and +1 attack range. As with all Ranged Cavalry, Dragoons can fire even while moving, which combined with their bonus damage against Civilians and Support Units, makes them raiders par excellence, only Light Cavalry being able to reach and neutralize Dragoons with ease. Dragoons also have a small chance to counterattack aircraft.
Foot Archers can also inflict serious damage to them, if they are able to get into reach, but any other unit type may have problems catching a troop of Dragoons that maneuvers well enough, and the slow Heavy Infantry in particular doesn't stand a chance. As with all other animal-borne cavalry units, the Dragoon can garrison inside Forts, but not inside Towers.