Model of Barrage Balloon, with mobile winch, hydrogen trailer and ground equipment, on base, scale 1:25

Model of Barrage Balloon with mobile winch, hydrogen trailer and ground equipment, on base, scale 1:25 Barrage balloons were used to protect land-based targets from low-flying aircraft. This forced the enemy aircraft to fly at heights of over 5000 feet where they could be attacked by anti-aircraft guns and fighter aircraft. The balloons, approximately 20,000 feet in capacity, were divided internally into two compartments by a fabric diaphragm, the lower compartment being the air space. As they ascended, the hydrogen in the upper compartment expanded, depressing the diaphragm.