The barrage balloon was simply a bag of lighter-than-air gas attached to a steel cable anchored to the ground. The balloon could be raised or lowered to the desired altitude by a winch. Its purpose was ingenuous: to deny low-level airspace to enemy aircraft. This simple mission provided three major benefits:

• forced aircraft to higher altitudes, thereby decreasing surprise and bombing accuracy;
• enhanced ground-based air defenses and the ability of fighters to acquire targets, since intruding aircrafts were limited in altitude and direction; and
• the cable presented a definite mental and material hazard to pilots.

Mindful of these capabilities, the British saw the barrage balloon as a viable mean to counter low-level attackers during the world wars.

During the last years of World War I, the British employed the barrage balloon in response to attacks by German Gotha bombers on London. The success of the barrage balloon in the First World War paved the way for its use in the Second. This time, however, instead of a mere handful, thousands of balloons dotted the British skies. Again, the balloons provided a partial solution in countering fast, low-flying German bombers and fighters and in protecting key installations. The British believed that an integrated air defense system should use every viable air defense weapon for self-protection - a combination that included the principal means of fighters, antiaircraft artillery and balloons. The only modification in balloon usage from World War I concerned the apron concept (more than one stuck on balloon). Instead, single balloons were used because they could be sent aloft more quickly and were easier to operate. Thus, in 1936 with war clouds darkening the horizons, the Committee of Imperial Defense authorized an initial barrage of 450 balloons for the protection of London.

With the capital securely covered, barrage balloons also flew at fleet anchorages and harbors from threatened areas. Although airfields also requested them during the early months of the war, the balloons were not available because of slow production and losses due to combat and bad weather. However, thanks to a new balloon plant, the barrage system had 2,368 balloons by the end of August 1940 and would maintain approximately 2,000 operational balloons until the end of the war.

These figures demonstrate the great value given by the British to the balloons. They had even formed Balloon Command in 1938, an independent command under the leadership of Air Marshal Sir E. Leslie Gossage, to control the 52 operational barrage balloon squadrons stationed across Great Britain. The Balloon Command was charged with the job of creating a barrage of huge balloons aimed at protecting British towns and cities, as well as key targets such as industrial areas, ports and harbors. They were made to protect everything at ground level from the threat of low-flying German dive-bombers. The barrage balloons, which were set at heights of up to 1,524 meters, would force these aircraft to fly high, making them less accurate, and bring them within range of the antiaircraft guns. Eventually, this command consisted of 33,000 men. The amount of equipment and the number of personnel, however, tell only part of the story. Performance in combat is the main indicator of a weapon system's success, and the balloons received a thorough test during World War II.

By the middle of 1940, there were 1,400 balloons, a third of them over the London area. By 1944 the number had risen to nearly 3,000. Later in the war, the barrage balloons were moved to combat the V-1 flying bomb.

The balloons were huge (on average, about 18.9 meters long and 7.6 meters in diameter), fixed to the things that being protected or from the back of lorries with a winch. By 1944 the balloons were moved to make up a ring around south London to combat the V-1 menace with a fair degree of success - as many as 100 V-1s snagged themselves on the balloons' cables. It was not all plain sailing, however. Some of the balloons were struck by lightning while others were shot down - 50 were shot down in one day when they were set up round Dover. (The Scottish physicist Arthur Vestry [1869-1959] later devised a method for protecting barrage balloons from lightning.)