German observation balloon. Hydrogen-filled German military observation balloon and two observers (in basket) being watched by soldiers during World War I (1914-1918). These balloons were used by both sides on the Western Front to direct artillery fire and survey enemy positions. This view is from around 1914 or 1915. Extensive trench systems were dug by both sides as the opposing armies fought to a standstill on the Western Front in northern France and Belgium. Many millions fought and died in what was one of the largest wars in history. This photograph is from the Bain News Service, one of the USA's earliest news picture libraries.