An observation balloon is a type of balloon that is employed as an aerial platform for gathering intelligence and spotting artillery. The use of observation balloons began during the French Revolution
British observation balloon from 1908, typical of pre-WWI observation balloons
The battle of Fleurus, 26 June 1794, saw the first military use of an aircraft (L'Entreprenant).
German Parseval-Siegsfeld type balloon at Équancourt (September 1916). The rear "tail" fills with air automatically through an opening facing the wind.
Caquot type kite balloon, used by the Allies in the mid-latter part of WWI
L'Intrépide is a hydrogen balloon of the Compagnie d'Aérostiers and is the oldest preserved manned aircraft in Europe.
L'Intrépide on display at the Heeresgeschichtliches Museum.
L'Intrépide or Hércule flown at the siege of Mainz (1795); print of 1890.