‘Windows’ was first used on July 25th 1943. On July 15th 1943, the War Cabinet, led by Winston Churchill, had given its consent for the use of ‘Windows’ and ten days later it was put into use. At 00.25 a formation of bombers flew over Heligoland on their way to Hamburg. All the bombers dropped ‘Windows’. A radar station on Heligoland code-named ‘Hummer’ reported its findings. Each cloud of foil remained effective for 15 minutes and according to ‘Hummer’ 11,000 bombers were flying en route to a target in Nazi Germany. ‘Hummer’ assumed that that Allies did not have 11,000 bombers and reported back that it “was disturbed by so many point-targets looking like aircraft, either stationary or slow moving. The picking up of genuine aircraft is made extremely difficult. Once they have been picked up it is possible to follow them, but only with difficulty.”
The next radar station along the route – codenamed ‘Auster’ – reported similar findings, as did all the rest on the route to Hamburg.
German night fighters were in the air awaiting instructions as to their flight routes, but such information was not forthcoming because each radar station was in chaos. Reported radio transmissions included:
“The enemy are reproducing themselves”
“It is impossible – too many hostiles.”
Wait a while. There are many more hostiles.”
“I cannot control you.”
“Try without your ground control.”
Without vital information coming to them from the ground, German night fighters were all but helpless – such was the impact of ‘Windows’.
When the attackers reached Hamburg on July 25th, they found that ground defences were in chaos. Searchlights homed in on non-existent attackers. Ground forces had been denied information as to where their expected targets were and “RAF crews made their bombing runs on an almost defenceless Hamburg”. (Alfred Price)
On this raid over Hamburg, the Allies could have expected a loss of 6% of their bombers. In fact only 1.5% were lost – 12 bombers –far below the expected loss of 50 aircraft. The success of this raid was put down to the confusion caused by ‘Windows’ – 92,000,000 strips had been dropped by the incoming bombers, which represented 40 tons of aluminium foil. The use of ‘Windows’ in subsequent raids on Hamburg was equally effective in allowing the bombers to get through and 9 square miles of the city were destroyed. The damage down was so great that the city’s civil defence chief, Major-General Kehrl, ordered all non-essential civilians to leave the city. It is estimated that 1 million did so.
The Germans quickly reorganised their defence against ‘Windows’. Close ground control – where units on the ground took over control of what was going on – was abandoned and two new night-fighting tactics were introduced: ‘Wild Boar’ and ‘Tame Boar’. ‘Wild Boar’ concentrated night fighters over the assumed target based on the flight pattern of the incoming bombers. Flares dropped by ‘Pathfinder’ bombers combined with the flames coming off bomber exhaust outlets were sufficient to give German night fighters a visual target. Because the pilots had a visual fix, the impact of ‘Windows’ was minimal. A development of ‘Wild Boar’ was ‘Tame Boar’ developed by Colonel von Lossberg, a night fighting expert. His system was for the radars on the ground to actually home in on ‘Windows’ and direct night fighters to where it was most dense. Lossberg assumed that the densest concentration of ‘Windows’ was bound to be where most bombers were. Once in the vicinity of the bombers, the night fighters reverted to ‘Wild Boar’ in that they used the flight path of the bombers to maintain contact with them and visual contact to attack them. ‘Wild Boar’ proved a highly effective tactic when the Allies attacked Nuremberg on March 30th 1944. A radar beacon to the south of Cologne called ‘Ida’ picked up the incoming flight and passed this information on to night fighters that were already airborne – coastal radar had already picked up the bombers. While Munich could have been a target, it soon became obvious that the bombers were flying somewhat to the northeast of Munich and Nuremberg was assumed to be the only feasible target. Two hundred night fighters attacked the incoming bombers using a visual fix as opposed to radar and 94 British Lancaster and Halifax bombers were lost were lost. German tactics were helped by the weather conditions that night: a very clear night with no clouds and a clear half moon that caused the vapour trails from the bombers engines to clearly stand out.
‘Windows’ lost its full effectiveness in the summer of 1943 when the Lichtenstein B/C and C-1 radar systems were replaced by the SN-2, which was capable of ‘seeing’ through ‘Windows’. However, even SN-2 had its failings as the speed of a night fighter carrying this system was compromised by 30 mph because of the size of the radar antennae carried on the aircraft. Also later in the war, Mosquito night fighters were equipped with ‘Serrate’ that allowed them to track German night fighters by following the emissions from their SN-2 sets.