An observation balloon, 1917 (c).

Observation balloons were used for intelligence gathering and artillery spotting. Observers would be carried in baskets or containers that hung underneath the balloons which were fixed by cables to the ground. By using a telephone, the wire of which ran down one of the cables, they could direct their own guns on to enemy troops, batteries and fortifications. Lantern slide from a box of 80 lantern slides associated with the Western Front, 1917.