The Caisson Platoon of the 3d United States Infantry “The Old Guard”. Old Guard Soldiers are in Arlington National Cemetery Daily Rendering Final Honors To Our Fallen, Both Past and Present.

The caissons were built in 1918, and used for 75mm cannons. They were originally equipped with ammunition chests, spare wheels, and tools used for the cannons. Today these have been removed and replaced with the flat deck on which the casket rests.

http://www.army.mil/info/organization/unitsandcommands/commandstructure/theoldguard/specplt/caisson.htm

During the American Civil War The caisson was also a two-wheeled carriage. It carried two ammunition chests and a spare wheel. A fully loaded limber and caisson combination weighed 3,811 pounds (1728.6 kg). The limbers, caissons, and gun carriages were all constructed of oak. Each ammunition chest typically carried about 500 pounds (226.8 kg) of ammunition or supplies. In addition to these vehicles, there were also battery supply wagons and portable forges that were used to service the guns.

http://en.wikipedia.org/wiki/Field_artillery_in_the_American_Civil_War

Photo 1 A caisson carries a casket with remains representing nine WW II Army Airmen during a burial ceremony at Arlington National Cemetery in Arlington, Va Credit Associated Press

Photo 2 Gibson’s Horse Battery (C. 3d U.S. Artillery) Near Fair Oaks, Virginia June 1862.