Balloon Basket, USA, World War I, United States Army Air Service

Military observers for the U.S. Army Air Service watched and photographed enemy troops from balloon baskets like this one. Flying close to the front lines, they reported details to commanders using telephone lines.  

The balloons were tethered to a winch on the ground and floated between 1,000 and 5,000 feet (305 and 1524 meters). Each held a vast volume of flammable hydrogen gas that could fill almost half of an Olympic-sized swimming pool.