Horse gas masks first came about around World War I to protect them from chemical agents. Amazing that we still used horses during warfare then! I do love how fitting them up with these crazy masks makes the little horsey look a lot more intimidating and apocalyptic. Gas masks have that effect. [Industrial Anatomy via Neatorama]
The US Calvary was a horse mounted regiment until the 1950s when it got absorbed into an artillery group. Horses are still used though, in places like Afghanistan, where the terrain is too rugged, or a low profile is a critical part of the mission. In the attached photo US Special Forces are seen mounted on horseback during 2001 in Operation Enduring Freedom in Afghanistan.