Underway replenishment
_Sailors_look_on_as_a_refueling_probe_crosses_over_the_South_China_Sea,5715.jpg")
![Early ship resupplying at sea, such as an attempt with HMS Captain in 1870, was slow and often hazardous.](/Images/godic/202502/18/HMS_Captain5715.jpg")
![Schematic for a Temperley transporter, a crane for hauling heavy loads, and used in early UR trials in 1898.](/Images/godic/202502/18/Temperley_Grab_For_Two_Rope_System,_1911.svg5715.png")
![Trials of the Metcalfe system in 1902 between the battleship HMS Trafalgar and collier.](/Images/godic/202502/18/Metcalfe_trial_19025715.jpg")
Underway replenishment (UNREP) (US Navy) or replenishment at sea (RAS) (North Atlantic Treaty Organisation/Commonwealth of Nations) is a method of transferring fuel, munitions, and stores from one ship to another while under way.