Diagram of instructions for operating type "B" Free Balloon Barrage Balloon, circa 1941

Diagram card providing written and visual instructions on how to set up and operate a type "B" Free Balloon Barrage Balloon.

Barrage balloons were used as an anti-aircraft defence to protect key ground targets, particularly from bombing attack. They often proved a hindrance to the flight path of enemy aircraft, increasing the likelihood of a collision and forcing opposition aerial forces to fly at a higher altitude. Due to the hydrogen that was used to lift the balloons, collisions and attacks from aircraft could result in significant explosions. Free barrage balloons were untethered and were allowed to naturally drift aerially towards opposition aircraft. Tethered barrage balloons by comparison, were typically held in place by cables tethered to concrete blocks.