International Maritime law states.
The following classes of enemy vessels are exempt from attack:
(a) hospital ships;
(b) small craft used for coastal rescue operations and other medical transports;
(c) vessels granted safe conduct by agreement between the belligerent parties including:... See More
(i) cartel vessels, e.g., vessels designated for and engaged in the transport of prisoners of war;
(ii) vessels engaged in humanitarian missions, including vessels carrying supplies indispensable to the survival of the civilian population, and vessels engaged in relief actions and rescue operations;
48. Vessels listed in paragraph 47 are exempt from attack only if they:
(a) are innocently employed in their normal role;
(b) submit to identification and inspection when required; and
(c) do not intentionally hamper the movement of combatants and obey orders to stop or move out of the way when required.
http://www.icrc.org/IHL.nsf/52d68d1...7694fe2016f347e1c125641f002d49ce?OpenDocument
The following classes of enemy vessels are exempt from attack:
(a) hospital ships;
(b) small craft used for coastal rescue operations and other medical transports;
(c) vessels granted safe conduct by agreement between the belligerent parties including:... See More
(i) cartel vessels, e.g., vessels designated for and engaged in the transport of prisoners of war;
(ii) vessels engaged in humanitarian missions, including vessels carrying supplies indispensable to the survival of the civilian population, and vessels engaged in relief actions and rescue operations;
48. Vessels listed in paragraph 47 are exempt from attack only if they:
(a) are innocently employed in their normal role;
(b) submit to identification and inspection when required; and
(c) do not intentionally hamper the movement of combatants and obey orders to stop or move out of the way when required.
http://www.icrc.org/IHL.nsf/52d68d1...7694fe2016f347e1c125641f002d49ce?OpenDocument