A collier is a bulk cargo ship designed to carry coal, especially for naval use by coal-fired warships. In the late eighteenth century, a number of wooden-hulled sailing colliers gained fame after being adapted for use in voyages of exploration in the South Pacific, for which their flat-bottomed hulls and sturdy construction made them well-suited. USS Langley, the first aircraft carrier in the United States Navy was a converted collier, fitted with a large elevated flat deck, used before the invention of purpose-built aircraft carrier hulls.
Coaling at sea was critical to navies and speed of coal transfer was an important metric of naval efficiency. In 1883, forty tons an hour was considered fast and it would take over twelve hours to restock half the bunkers of a typical ship, HMS Collingwood (1882).