Observation balloons are balloons that are employed as aerial platforms for intelligence gathering and artillery spotting. Their use began during the French Revolutionary Wars, reaching their zenith during World War I, and they continue in limited use today.
Historically, observation balloons were filled with hydrogen. The balloons were fabric envelopes filled with hydrogen gas, whose flammable nature led to the destruction of hundreds of balloons on both sides. Observers manning these observation balloons frequently had to use a parachute to evacuate their balloon when it came under attack. To avoid the potentially flammable consequences of hydrogen, observation balloons after World War I were often filled with non-flammable helium.
Typically, balloons were tethered to a steel cable attached to a winch that reeled the gasbag to its desired height (usually 1,000-1,500 metres) and retrieved it at the end of an observation session.
