Columbia subject headings:
Chemical warfare--History--20th century.
World War, 1914-1918--Chemical warfare.
World War, 1939-1945--Chemical warfare.
Harvard subject headings:
World War, 1939-1945--Chemical warfare.
World War, 1939-1945--Germany.
Princeton subject headings:
Chemical warfare--History--20th century.
World War, 1914-1918--Chemical warfare.
World War, 1939-1945--Chemical warfare.