Hi Frank,
das waren „barrage balloons“: Ballons, die die „doodlebugs“ (deutsche Raketen) auffangen sollten. Ich weiß nicht, wie gut Dein Englisch ist, aber vielleicht hilft das hier:
The people of Britain called the V1 missiles ‚Buzz Bombs‘ or ‚Doodlebugs‘. The first was dropped at Swanscombe in Kent on 13 June 1944 and the last one at Orpington in Kent on 27 March 1945. During that time, 6,725 were launched at Britain. Of these, 2,340 hit London, causing 5,475 deaths, with 16,000 injured. Three lines of defence were put in place against the missiles: fighter planes over the English coast, anti-aircraft batteries in Kent and barrage balloons around London. These were successful in destroying 3,500 V1 missiles.
Viele Grüße
MacD