A major purpose of the ships was initially to support the U.S. military during the Cold War, and they were designed with capabilities for that role, including using nuclear power instead of oil for greater endurance when deployed in blue water, and the ability to make adjustments to the carriers' weapons systems on the basis of new intelligence and technological developments. They were initially categorized only as attack carriers, but ships have been constructed with anti-submarine capabilities since . As a result, the ships and their aircraft are now able to participate in a wide range of operations, which can include sea and air blockades, mine laying, and missile strikes on land, air and sea.