The Hague Convention on Hospital Ships is a 1904 multilateral treaty that supplemented the 1899 Hague Convention for the adaptation to Maritime Warfare of the Principles of the Geneva Convention. The convention established that during times of war, hospital ships would be exempted from dues and taxes imposed on vessels in the ports of the states that ratify the treaty. It is the one treaty on the laws of war that was concluded between the two conferences at The Hague in 1899 and 1907.
Hague Convention on Hospital Ships Wikipedia
The Hague Convention on Hospital Ships was concluded on 21 December 1904 and entered into force on 26 March 1907. It was signed by 26 states and as of 2014 it is in force for 30 states. One state—Serbia—signed the treaty but has not ratified it. The convention remains in force for the states that ratified it.