Here is a quote from "Prize of War" on Wikipedia:
"Prizes of war at sea are unlikely in major modern conflicts due to changes in the way wars are fought and financed, international law and oversight, and the possibility of a prize being booby trapped. However the Hague Conventions of 1899 and 1907 do allow for war material to be claimed as trophies of war as does US law."
Since the 1907 one was the one they were under, as it wasn't updated until 1954, the convention said:
"Article 56 of the Hague Convention of 1907, stated:
"The property of municipalities, that of institutions dedicated to religion, charity and education, the arts and sciences, even when State property, shall be treated as private property.
"All seizure of, destruction or willful damage done to institutions of this character, historic monuments, works of art and science, is forbidden, and should be made the subject of legal proceedings."
Nowhere does it state anything about an instrument of war or a weapon. This is how the US got out from under Project Paperclip, plus they called it war reparations too.
Prize of war:
Hague Conventions of 1899 and 1907:
Hague Convention of 1954 (PDF):
War Trophies, Intro to law of war, US: