Soldiers would use their mounts in training, and so in the process habituate them to the physical and mental stresses of battle. In "The Training of Cavalry Remount Horses" from 1861, a method now known as counter-conditioning--in which an unpleasant sound, in this case a gunshot, was combined with a desirable reward such as food--was suggested. The soldier would tie the horse and discharge his firearm at a distance, then reward the horse, and calmly repeat until the horse would stand without being tied: "[B]e quite quiet yourself, and the horse will soon follow your example... Walk off to the front, fire, returning to the horse with something in your hand, bread or salt" (pg. 42). A similar technique is described in "A hand book for cavalry" from 1814: "[The horse] should be taught to stand the noise of drums, trumpets, and the fire of small arms. These objects are very easily and certainly accomplished, if managed with address and patience... a flash of priming from a pistol may constantly be used for several days at the same time... frequently the flint snapped to give fire while he feeds; and accompanied by caresses and kind sounds of the voice" (pg. 30)

The sheer exposure to combat activities would also familiarize the horses, with or without intentional reinforcement. In this 1930's clip of the German Potdam Riding School mounted police, at 0:45 they are shown standing up on their horses backs, firing off their rifles, and repeating. Around 1:00 they ride their horses over jumps, again while firing their rifles.