and offloading units (FPSOs). Replenishment ships Replenishment ships, known as oilers in the United States and fleet tankers in Commonwealth countries, are ships that can provide oil products to naval vessels while on the move. This process, called underway replenishment, extends the length of time a naval vessel can stay at sea, as well as her effective range. Prior to underway replenishment, naval vessels had to enter a port or anchor to take on fuel. In addition to fuel, replenishment ships may also deliver water, ammunition, rations, stores and personnel. Ore-bulk-oil carriers An ore-bulk-oil carrier, also known as combination carrier or OBO, is a ship designed to be capable of carrying wet or dry bulk cargoes. This design was intended to provide flexibility in two ways. Firstly, an OBO would be able to switch between the dry and wet bulk trades based on market conditions. Secondly, an OBO could carry oil on one leg of a voyage and return carrying dry bulk, reducing the number of unprofitable ballast voyages it would have to make. In practice, the flexibility which the OBO design allows has gone largely unused, as these ships tend to specialize in either the liquid or dry bulk trade. Also, these ships have endemic maintenance problems. On one hand, due to a less specialized design, an OBO suffers more from wear and tear during dry cargo onload than a bulker. On the other hand, components of the liquid cargo system, from pumps to valves to piping, tend to develop problems when subjected to periods of disuse. These factors have contributed to a steady reduction in the number of OBO ships worldwide since the 1970s. One of the more famous OBOs was of which in September 1980 became the largest British ship ever lost at sea. It sank in a Pacific typhoon while carrying a cargo of iron ore from Canada to Japan. Floating storage units Floating storage and offloading units (FSO) are used worldwide by the offshore oil industry to receive oil from nearby platforms and store it until it can be offloaded onto oil tankers. A similar system, the floating production storage and offloading unit (FPSO), has the ability to process the product while it is on board. These floating units reduce oil production costs and offer mobility, large storage capacity, and production versatility. FPSO and FSOs are often created out of old, stripped-down oil tankers, but