[Exakt]

Originally Posted by pickinthebanjo

Ok, I knew it had something to do with detering plains. Thats an interesting device

Here is some more info:

In 1938 the British Balloon Command was established to protect cities and key targets such as industrial areas, ports and harbours. Balloons were intended to defend against dive bombers flying at heights up to 5,000 feet (1500 m), forcing them to fly higher and into the range of concentrated anti-aircraft fire—anti-aircraft guns could not traverse fast enough to attack aircraft flying at low altitude and high speed. By the middle of 1940 there were 1,400 balloons, a third of them over the London area.
While dive-bombers were devastatingly effective against undefended targets, such as Guernica and Rotterdam, they were very vulnerable to attack by fighter aircraft, and their use by Germany against Britain with its effective Royal Air Force was rapidly discontinued. Balloons proved to be of little use against the German high-level bombers with which the dive-bombers were replaced, but continued to be manufactured nonetheless, until there were almost 3,000 in 1944. They proved to be mildly effective against the V-1 flying bomb, which usually flew at 2,000 feet (600 m) or lower but had wire-cutters on its wings to counter balloons.[citation needed] Two hundred and thirty-one V-1s are officially claimed to have been destroyed by balloons[1].