RAS is a method of transferring fuel, munitions, and stores from one ship to another while under way. Replenishment At Sea (RAS) was initially carried 
out using a system of ropes and pulley blocks from the stern of the supply ship to the bow of the receiving ship. At this time, only stores and bags of 
coal were passed to the receiving ship.

RAS

Heavy jackstay	Light jackstay

FAS

In this method, the receiving ship follows directly behind the supplying ship. The fuel-supplying ship throws a marker buoy into the sea and the receiving ship takes station with it. Then the delivering ship trails a hose in the water that the fuel-receiving ship retrieves and connects to in order to receive fuel.