What was the purpose of the inflatable bombs attached to strings that floated above ships and other structures during war time?

The aim of barrage balloons was to protect valuable strategic targets from air attacks. The balloons were attached to the ground by thick cables - an aircraft running into them would not have a good day. Some models even carried explosive charges to increase the lethality. They were effective against low level attacks, but bombers could simply fly over them. However, this was not as big an advantage as it seemed. Flying higher reduced bombing accuracy, and forced aircraft to altitudes where AA fire was more effective. Balloon barrages were typically used to protect large, fixed targets such as factories and harbours - as the positions of these was typically known from pre-war intelligence, there was no risk of giving away their location.