Many present-day naval vessels, aside from aircraft carriers and full-length deck amphibious assault ships, are capable of carrying aircraft. A majority of United States Navy ships have at least a helipad, capable of landing medium-sized helicopters. Many others have decks and even hangars incorporated into the structure of the ship. It has become a standard part of modern ship design to have a deck that supports multiple, medium or large helicopters, as well as being able to house them in a hangar, for protection and maintenance. Aside from carriers and full-length deck amphibious assault ships, the US Navy has 12 classes of commissioned surface warships, 10 of which are aviation-capable. Two of those classes, patrol ships and mine counter-measure ships, are due to be replaced by the Litt