A vital part of the UK air defences during the Second World War were barrage balloons.
Large structures, about 19 metres long and eight metres in diameter, they were part-filled with hydrogen and deployed to altitudes of up to 5,000ft. They were very effective against aerial assaults. Flying into one, or into the taught ropes they were tethered to, could easily down an aircraft.
This forced the German Luftwaffe to fly higher – which prevented dive bombing, reduced the risk of surprise attacks and increased the time Allied fighter planes had to engage with the enemy.
By 1940, some 2,400 balloons were in position above towns, cities, industrial heartlands and ports across Britain. Specialist barrage balloon squadrons were formed, often staffed by women. They were responsible for maintaining, refilling and deploying the huge canvas structures on a daily basis.
Nineteen gasworks adapted their processes to make highly pure hydrogen for these balloons. One of these works, in Cambridge, produced 135 million cubic feet of gas between 1942 and 1944, enough to fill 7,500 balloons.
Barrage balloons were effective too against flying bombs (also known as buzz bombs, or doodlebugs) which emerged during the latter stages of the war. Over an 80-day period, a screen of 2,000 barrage balloons assembled around London destroyed 279 of these early cruise missiles.
We’ve worked with Professor Russell Thomas, chairman of the history panel of the Institution of Gas Engineers and Managers, to produce this special series of stories for #VEDay75.