Columbia subject headings:
Harvard subject headings:
Somme (France)--History, Military--20th century.
Somme, 1st Battle of the, France, 1916
Somme, 2nd Battle of the, France, 1918.
World War, 1914-1918--Aerial operations
Princeton subject headings:
Somme (France)--History, Military--20th century.
Somme, 1st Battle of the, France, 1916.
Somme, 2nd Battle of the, France, 1918.
World War, 1914-1918--Aerial operations.