Aviation in World War I, Zeppelin, Rigid airship, Interrupter gear, Monoplane, Battle of the Somme, Battle of Albert (1916), First day on the Somme, Battle of Bazentin Ridge, High Wood, Bazentin, Battle of Pozières, Battle of Guillemont, Battle of Ginch, Battle of Flers-Courcelette, Battle of Morval, Battle of Thiepval Ridge, Battle of Le Transloy, Battle of the Ancre Heights, Battle of the Ancre, List of Canadian battles during the First World War, Bloody April, Anti-aircraft warfare, Observation balloon