Underway replenishment

INS Deepak (left) conducts a RAS with INS Vikrant.

Underway replenishment (UNREP) (U.S. Navy) or replenishment at sea (RAS) (North Atlantic Treaty Organization/Commonwealth of Nations) is a method of transferring fuel, munitions, and stores from one ship to another while under way. First developed in the early 20th century, it was used extensively by the United States Navy as a logistics support technique in the Pacific theatre of World War II, permitting U.S. carrier task forces to remain at sea indefinitely.