A small, non-nuclear aircraft carrier requires approximately 400,000 litres of fuel per day. If a ship on the open sea needs filling up, refuel ships come into play. During the tricky procedure, both ships must keep at least 30 metres apart – otherwise a dangerous phenomenon known as the Venturi effect could occur. As the vessels displace water into the space between them, the flow increases in speed, which reduces water pressure and leads to a suction effect. This draws the ships towards one another. During the refuelling process, a cable is catapulted from the tanker to the aircraft carrier and fixed in place. This is connected to the fuel tube, which pumps up to 3,800 litres of diesel per minute into the warship’s fuel tank.