a chest to hold ammunition.-a four-wheeled carriage for conveying ammunition, consisting of two parts, a body and a limber. in light field batteries there is one caisson to each piece, having two ammunition boxes on the body, and one on the limber.-a chest filled with explosive materials, to be laid in the way of an enemy and exploded on his approach.-a water-tight box, of timber or iron within which work is carried on in building foundations or structures below the water level.-a hollow floating box, usually of iron, which serves to close the entrances of docks and basins.-a structure, usually with an air chamber, placed beneath a vessel to lift or float it.-a sunk panel of ceilings or soffits.