A joint support ship (JSS) is a multi-role naval vessel capable of launching and supporting joint amphibious and airlift operations. It can also provide command and control, sealift and seabasing, underway replenishment, disaster relief and logistics capabilities for combined land and sea operations. Background The preliminary ideas for joint support ships arose from the development of "helicopter carriers", classes of vessels such as landing platform docks (LPDs) and landing helicopter docks (LHDs) designed for the operation of rotary-wing and other types of vertical take-off and landing (VTOL) aircraft. Unlike conventional fixed-wing aircraft carriers, these vessels do not require steam catapults for the launching of aircraft or arresting cables for the recovery or aircraft, and thus provided more space below the flight deck which could be utilised for other purposes. Some early LHDs were converted World War II-era aircraft carriers such as the United States Navy (USN)'s Essex-class vessels, but later designs often featured non-full length flight decks, usually at rear of the vessel. While initial emphasis was placed upon airborne operations, as the need for combined forces capabilities grew, facilitating amphibious operations also became a requirement, and later designs such as the Royal Navy (RN)'s LPD emerged featuring a well dock to launch and recover personnel, vehicular and utility landing craft, and in the case of the USN's LPD, landing helicopter assault (LHA) and other similar classes of vessels, tracked amphibious landing vehicles such as the AAVP-7A1. To support the air- and sea-going craft these vessels carried, they often featured fuel bunkers with increased storage capacity, and were often utilised as supplementary auxiliary ships to provide underway replenishment (UNREPs) to other vessels. Their absence of large calibre weapons on weather decks and with increased storage space below, they also proved very useful at sealift operations. Many also had onboard hospital facilities and the vessels served as casualty evacuation vessels. These multiple roles were demonstrated in 1956 during the Suez crisis, where the helicopters of , a former World War II aircraft carrier repurposed to a helicopter carrier, were not only used to transport Royal Marines to the shore but supplies and other cargo as well, and return with wounded troops. With a combination of army (or marine) and navy personnel and aircrew onboard, and often equipped with a wide range of sensor suites, these vessels were utilised as ad-hoc or formal joint command and control centres, as demonstrated during the