Columbia subject headings:
Tunneling--Europe--History--20th century.
World War, 1914-1918--Engineering and construction.
World War, 1914-1918--Trench warfare.
World War, 1914-1918--Tunnel warfare.
Harvard subject headings:
Tunneling--Europe--History--20th century.
World War, 1914-1918--Engineering and construction.
World War, 1914-1918--Trench warfare.
World War, 1914-1918--Tunnel warfare.
Princeton subject headings:
Tunneling--Europe--History--20th century.
World War, 1914-1918--Engineering and construction.
World War, 1914-1918--Trench warfare.
World War, 1914-1918--Tunnel warfare.