I was referring to the general surveillance of opposing forces by governments. Even still, balloons have been used for surveillance and attack for over one hundred years.
During the siege of Yorktown in 1862, Union General Fitz Porter decided to do some surveillance using only one rope on an observation balloon. The rope snapped and he drifted over enemy lines. Confederates tried to shoot him down but missed. Eventually the wind sent him back over Union lines.
Balloons were used in WW1 as observation posts (ushering in wide-spread use of parachutes) and in WW2 for both observation and area over-flight denial.
By May 1945, Japan sent almost 10,000 armed balloons across the pacific. They were largely ineffective, however, they did kill a pregnant mother and five children who discovered a downed balloon in Bly, Oregon. 285 Japanese balloons were recovered, one as far east as Texas.
