Prize rules Prize rules or cruiser rules govern the taking of prizes : vessels captured on the high seas during war . They are intertwined with the blockade rules . Customary rules were originally laid down in the days of sailing ships . These were supplemented by various international agreements including the Declaration of Paris ( 1856 ) and the Hague Conventions ( 1899 and 1907 ) and other naval agreements during the 20th century . Although these rules are still part of the laws of war , changes in technology like the radio and the submarine made them redundant between belligerents during World War I and World War II . Still , the Nuremberg Tribunal found that these rules were still applicable to neutral merchant shipping . Prize rules state that passenger ships may not be sunk , crews of merchant ships must be placed in safety before their ships may be sunk ( life boats are not considered a place of safety unless close to land ) , only warship s and merchant ships that are a threat to the attacker may be sunk without warning . Declaration of Paris , 1856 . In 1856 and afterward , numerous states , including the United Kingdom , Austria - Hungary , France , Prussia , Russia , Sardinia and the Ottoman Empire , ratified the Declaration of Paris . It regulated the relationship between neutral and belligerent and shipping on the high seas when the signatories were fighting each other , but not when fighting non - signatory nations . The United States withheld its formal adherence in 1857 . The Rules . Part IV , Art . 22 of the Treaty for the Limitation and Reduction of Naval Armaments , relates to submarine warfare . It states as follows : 20th century . All sides signed treaties ( the Hague Conventions of 1899 and 1907 ) subscribing to rules of prize warfare before World War I and they were also in effect during World War II . During 1914 - 1917 , Germany adhered to the prize rules , until it declared unrestricted submarine warfare . During World War II , Germany adhered to the prize rules for the first 2 months of the conflict in 1939 before turning again to unrestricted submarine warfare . In 1912 , British Admiral Sir John " Jackie " Fisher , by then a retired First Sea Lord , presented a paper to the . He developed the argument that submarine s would find adherence to prize rules impossible , for practical reasons : a submarine could not capture a merchant ship , for it would have no spare manpower to deliver the prize to a neutral port , neither could it take survivors or prisoners , for lack of space . " " . . . there is nothing a submarine can do except sink her capture . " " If a merchant ship were armed , as was permitted by a conference in London in 1912 , then a submarine was under more pressure to destroy a ship . He asked : " " What if the Germans were to use submarines against commerce without restriction ? " " This last comment was thought to be unsupportable . Winston Churchill , then First Lord of the Admiralty and political head of the Royal Navy , supported by senior naval opinion , said it was inconceivable that " " . . . this would ever be done by a civilised power . " " However it was Fisher who was proven correct . The treaties are still in effect today .