The Tankers are the energy source for the Navy. Without them, the fleets would all become immobile, as the Japanese Navy found out during WWII.
Refueling at sea can be a precarious and arduous task and requires
expert seamanship from both skippers for such a manouevre. But a steady
course brings H.M.S Wave Sovereign along side H.M.A.S Sydney to commence
refueling in Korean waters.
Sydney will herself will pass on parts of her precious load to fleet fighting vessels in turn.