<P> While dive - bombing was a devastatingly effective tactic against undefended targets, such as Guernica and Rotterdam, dive - bombers were very vulnerable to attack by fighter aircraft while performing a dive, and their use in this role by Germany against the UK 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. 231 V - 1s are officially claimed to have been destroyed by balloons . </P> <P> The British added two refinements to their balloons, "Double Parachute Link" (DPL) and "Double Parachute / Ripping" (DP / R). The former was triggered by the shock of an enemy bomber snagging the cable, causing that section of cable to be explosively released complete with parachutes at either end; the combined weight and drag bringing down the aircraft . The latter was intended to render the balloon safe if it broke free accidentally . The heavy mooring cable would separate at the balloon and fall to the ground under a parachute; at the same time a panel would be ripped away from the balloon causing it to deflate and fall independently to the ground . </P> <P> In January 1945, during Royal Navy Fleet Air Arm raids on the Palembang oil refineries, the British aircrews were surprised by massive use of barrage balloons in the Japanese defences . These were spherical and smaller than the British type . One Grumman Avenger was destroyed, and crew killed, from striking a balloon cable . </P> <P> In 1942 Canadian and American forces began joint operations to protect the sensitive locks and shipping channel at Sault Ste . Marie along their common border among the Great Lakes against possible air attack . During severe storms in August and October 1942 some barrage balloons broke loose, and the trailing cables short - circuited power lines, causing serious disruption to mining and manufacturing . In particular, the metals production vital to the war effort were disrupted . Canadian military historical records indicate that one of the more serious incidents recorded, known as "The October Incident", caused an estimated loss of 400 tons of steel and 10 tons of ferro - alloys produced for the war effort . This was determined to be caused, in part, by winter weather . This incident resulted in a large loss of vital materials intended to help the war effort ." </P>

What were blimps used for in world war 2