Learn more about Caisson (military)
 Design and use
Fundamentally it is a big box mounted lengthwise along an axle that has a road wheel at each end. Rigidly attached to the middle of the axle is a pole to each side of which a horse is harnessed. The whole is therefore a very basic horse-drawn vehicle. The pole is properly called a limber and it is this which gives the vehicle its British name. The vehicle is used for towing a gun mounted on a similar carriage but with the gun's trail taking the place of the pole. In order to move the whole assembly at consistently high speeds, two further horses are required. These are harnessed with long traces back to the limber.
The box has simple seats on it for the driver and crew. It contains ammunition. The whole is designed so that it can be brought up to its firing position and the three units - gun, limber and horses - rapidly separated so as to bring the gun promptly into action with the horses at a distance, out of harm's way but ready for the withdrawal phase of the action.
In the accompanying photograph, the pole which is the limber proper appears black between the two wheel-horses. The vehicle appears to be specially constructed for funerals but in the military version, the units represented are the limber (caisson), to the left and to it is hitched the trail of the gun, here replaced by a trailer of similar configuration, carrying the coffin (casket). Thus, strictly speaking the coffin is on a symbolic gun-carriage rather than on a symbolic caisson.
 The caisson in American and British culture
The song "The Caissons Go Rolling Along", written during the occupation of the Philippines by the United States of America refers to these; the version adopted as the United States Army's official song has, among other changes, replaced the word caissons with Army.
Caissons are also used during United States presidential funerals to carry the casket of the deceased president. When the equipage is used in this way for a state funeral in Britain, the coffin is usually placed on a platform mounted on top of the gun and referred to as being carried on a gun carriage. For the funerals of British kings, there is a tradition that the horses be replaced by a detail from the Royal Navy.