Limbers and caissons

A limber is a two-wheeled cart designed to support the trail of an artillery piece, or the stock of a field carriage such as a caisson or traveling forge, allowing it to be towed.

A caisson is a two-wheeled cart designed to carry artillery ammunition. The British term was "ammunition wagon". Caissons are used to bear the casket of the deceased in some state and military funerals in certain Western cultures, including the United States.

As artillery pieces developed trunnions and were placed on carriages featuring two wheels and a trail, a limber was devised. This was a simple cart with a pintle. When the piece was to be towed, it was raised over the limber and then lowered, with the pintle fitting into a hole in the trail. Horses or other draft animals were harnessed in single file to haul the limber. There was no provision for carrying ammunition on the limber, but an ammunition chest was often carried between the two pieces of the trail.

The British developed a new system of carriages, which was adopted by the French, then copied from the French by the United States.

During the American Civil War, U.S. Army equipment was identical to Confederate Army equipment, essentially identical to French equipment, and similar to that of other nations. The field artillery limber assumed its archetypal form – two wheels, an ammunition chest, a pintle hook at the rear, and a central pole with horses harnessed on either side. The artillery piece had an iron ring (lunette) at the end of the trail. To move the piece, the lunette was dropped over the pintle hook (which resembles a modern trailer hitch). The connection was secured by inserting a pintle hook key into the pintle.

...
Wikipedia