To extend the duration of stay at sea, every cubic centimetre of space on navy and research vessels is utilised. All available spaces and any inaccessible places on the ship are used as additional tanks for drinking water, diesel or aviation fuel. The tank shape and dimensions are completely different from familiar standard tanks. Depending on the type and size of the ship, they can also extend over several decks. A reliable level measurement is indispensable for the operation of these ships.