Some of the earliest military drones appeared in the mid-1850s. The concept of drones may well date back to 1849, when Austria attacked Venice using unmanned balloons stuffed with explosives(Fig. 1). Austrian forces, who were besieging Venice at the time, launched around 200 of these incendiary balloons over the city. Each balloon carried anywhere between 24 (11 kg) to 30 (14 kg) pounds of bombs.
As innovative as this event was in the field of military technology, the use of balloons does not really meet the current definition of drones, especially military drones, as we have seen above. After WW1, UAV technological developments continued unabated. In the 1930s, the U.S. Navy began experimenting with radio-controlled aircraft, which resulted in the development of Curtiss N2C-2 Drone in 1937.
In 1935, the British developed “Queen Bee”, a radio-controlled target drone, which is also believed to have led to the use of term “drone,” for radio-controlled unmanned aircrafts.
Radioplane OQ-2, a remote-controlled model airplane developed by British actor Reginald Denny and engineer Walter Righter in the 1930s, actually became the first mass-produced UAV product in the U.S. Nearly 15,000 drones were manufactured for the military during the war.