A hospital ship is a ship designated for primary function as a floating medical treatment facility or hospital. Most are operated by the military forces (mostly navies) of various countries, as they are intended to be used in or near war zones.
International law 
- Ship must be clearly marked and lighted as a hospital ship
- The ship should give medical assistance to wounded personnel of all nationalities
- The ship must not be used for any military purpose
- The ship must not interfere with or hamper enemy combatant vessels
- Belligerents, as designated by the Hague Convention, can search any hospital ship to investigate violations of the above restrictions
- Belligerents will establish the location of a hospital ship
According to the San Remo Manual on International Law Applicable to Armed Conflicts at Sea, a hospital ship violating legal restrictions must be duly warned and given a reasonable time limit to comply. If a hospital ship persists in violating restrictions, a belligerent is legally entitled to capture it or take other means to enforce compliance. A non-complying hospital ship may only be fired on under the following conditions:
- Diversion or capture is not feasible
- No other method to exercise control is available
- The violations are grave enough to allow the ship to be classified as a military objective
- The damage and casualties will not be disproportionate to the military advantage.
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Such ships possibly existed in ancient times. The Athenian Navy had a ship named Therapia, and the Roman Navy had a ship named Aesculapius, their names indicating that they may have been hospital ships. During the 17th century, it became customary for naval squadrons to be accompanied by special vessels with the job of taking in the wounded after each engagement. On 8 December 1798, unfit for service as a warship, HMS Victory was ordered to be converted to a hospital ship to hold wounded French and Spanish prisoners of war. Another early example of a hospital ship was USS Red Rover in the 1860s, which aided the wounded soldiers of both sides during the American Civil War. It was the sighting by the Japanese of the Russian hospital ship Orel, correctly illuminated in accordance with regulations, that led to the Battle of Tsushima during the Russo-Japanese War. Orel was retained as a prize of war by the Japanese after the battle. During World War I and World War II, some passenger liners were converted for use as hospital ships. RMS Aquitania and HMHS Britannic were two examples of ships serving in this capacity.
The last British Royal Yacht, the post World War II HMY Britannia, was ostensibly constructed in a way as to be easily convertible to a hospital ship, but this is now thought to be largely a ruse to ensure Parliamentary funding, and she never served in this role - reputedly her lifts were too small to take standard-sized stretchers.
A development of the Lun-class ekranoplan was planned for use as a mobile field hospital for rapid deployment to any ocean or coastal location at a speed of 297 knots (550 km/h). Work was 90% complete on this model, the Spasatel, but Soviet military funding ceased and it was never completed.
The Brazilian Navy currently also operates several hospital ships on the Amazon and its tributaries. The Brazilians have an innovative and well-developed program of small, shallow-draft hospital ships that can provide medical care to the people in the interior of the vast Amazon region.
The first purposely built hospital ship in the US Navy was the USS Relief which was commissioned in 1921. Most hospital ships in the US Navy during World War II were converted passenger liners. And most were not marked as neither the Japanese or Germans were concerned with the Hague Convention on hospital ships.
The U.S. Navy's two current hospital ships, the USNS Mercy (T-AH-19) and USNS Comfort (T-AH-20), are operated by Military Sealift Command. Their primary mission is to provide emergency on-site care for U.S. combatant forces deployed in war or other operations. The ships' secondary mission is to provide full hospital services to support U.S. disaster relief and humanitarian operations worldwide.
Each ship contains 12 fully equipped operating rooms, a 1,000-bed hospital facility, digital radiological services, a medical laboratory, a pharmacy, an optometry lab, an intensive care ward, dental services, a CT scanner, a morgue, and two oxygen-producing plants. Each ship is equipped with a helicopter deck capable of landing large military helicopters. The ships also have side ports to take on patients at sea.
The ships are converted San Clemente-class supertankers. Mercy was delivered in 1986 and Comfort in 1987. Normally, the ships are kept in a reduced operating status in Norfolk, Virginia, and San Diego, California, by a small crew of civil service mariners and active-duty navy medical and support personnel. Each ship can be fully activated and crewed within five days. For example, the Comfort departed Baltimore for Haiti on January 16, 2010, to provide relief to victims of the country's massive earthquake four days after it hit.
Legal status 
Modern hospital ships display large Red Crosses or Red Crescents to signify their Geneva convention protection under the laws of war. Even so, marked vessels have not been completely free from attack. During both world wars (see List of hospital ships sunk in World War I and in World War II), noncombatant markings did not stop the sinking of a number of hospital ships by either side. In one peculiar case, a British air attack in 1945 sank the German ship SS Deutschland with substantial loss of life. In the war's closing days, this ship may have been in the process of conversion to a hospital ship. If so, it apparently had not been sufficiently marked as a hospital ship, perhaps owing to the chaos surrounding the collapse of military and civilian authority in Nazi Germany.
Some hospital ships, such as the SS Hope, belong to civilian agencies, and as such are not part of any navy.
Armed vessels are disqualified from protection as a hospital ship under international law.
See also 
- List of Australian hospital ships
- Type 920 hospital ship
- List of hospitals and hospital ships of the Royal Navy
- Hospital Ships of the Sanitary Commission
- List of United States Army hospital ships
- List of US Navy hospital ships
- List of Brazilian Navy hospital ships
- List of hospital ships sunk in World War I
- List of hospital ships sunk in World War II
- Mercy Ships
- MS Jutlandia
- Ambulance#Military use
- Type 920 Hospital Ship
- Hospital train
- Hague Convention on Hospital Ships
- Hospital Ship (definition via WordNet, Princeton University)
- "Convention for the adaptation to maritime war of the principles of the Geneva Convention". Yale University. October 18, 1907. Retrieved August 2, 2009.
- "Modern Hospital Sails With U.S. Fleet." Popular Science Monthly, August 1927, p. 35.
- This article incorporates text from the public domain Dictionary of American Naval Fighting Ships. The entry can be found here.
- World Wide Hospital Ships
- Australian War Memorial - Sinking of the Centaur
- WW2 US Hospital Ships
- US Army Hospital Ships in WWII
Media related to Hospital ships at Wikimedia Commons