5924534 British soldiers putting up an observation balloon, c.1917 (b/w photo) by Unknown photographer, (20th century); National Army Museum, London; (add.info.: British soldiers putting up an observation balloon, c.1917 Photograph, World War One, Middle East (1914-1918), Palestine c.1917 Observation balloons were used extensively during World War One (1914-1918) for aerial reconnaissance and artillery flash-spotting. Placing observers on balloons behind the front lines and at height allowed the Army to locate targets at greater range than they could on the ground From a collection of photographs taken by Corporal Joseph Egerton, Shropshire Yeomanry in Sinai and Palestine.); by National Army Museum ; out of copyright.