A sudden closure involves the rapid sealing of a tidal inlet or breach in a dike. This is typically prepared in such a manner that the gap can be entirely closed in one swift action during slack tide. The use of caissons or sluice caissons is common, though other unique methods, such as sandbags or ships, have also been employed. Caissons were initially utilized as an emergency response for sealing dike breaches post the Allied Battle of Walcheren in 1944 and subsequently after the 1953 North Sea flood. This technique has since been refined and applied in the Delta Works projects.