Replenishment at Sea

Drawing of trials with the Metcalfe system with the battleship HMS Trafalgar and an unidentified collier. Royal Navy illustration.


Keeping ships and their crews supplied on long voyages has always been a difficult task, and as countries became empires with far-flung possessions, this became even more important. In the late 1800s, both the US and British began experiments with replenishing their ships at sea. Shore-based coaling stations were vulnerable to attack or sabotage, but ships could, in theory, move out of harms way. Some experiments with the battleship HMS Captain were unsuccessful, but Lieutenant (later admiral) Robert Lowry suggested a pulley system that would use watertight containers. While the Admiralty rejected his proposal, numerous similar ideas were floated in the few decades. The French may have been the first to conduct successful experiments with underway replenishment, using an overhead crane. In the early 1900s a Royal Navy engineer named Metcalfe came up with a pulley system that used a steam engine to maintain tension and move supplies between ships. Trials with the Metcalfe system achieved a transfer rate of 47 tons per hour, more than double previous capabilities. All these experiments had been with ships one behind the other, but eventually, some navies began experimenting with side-by-side replenishment. This offered a few advantages, such as more room to transfer supplies at the same time, and less likelihood that the transfer lines would get tangled in the ship's propellers if they fell into the water. However, they also required a steadier hand on the helm, since the water moving between the ships will tend to draw them together. By the time of World War II, most of the major navies had underway replenishment systems, which would prove crucial in the war at sea, particularly in the Pacific. It remains a mainstay of all global navies to this day.