Editing V-1 flying bomb (section)

===Deception===
To adjust and correct settings in the V-1 guidance system, the Germans needed to know where the V-1s were impacting. Therefore, [[Abwehr|German intelligence]] was requested to obtain this impact data from their agents in Britain. However, [[Double Cross System|all German agents in Britain had been turned]] and were acting as double agents under British control.{{Citation needed|date=January 2021}}

[[File:Flying Bomb- V1 Bomb Damage in London, England, UK, 1944 D21237.jpg|thumb|Aftermath of a V-1 bombing, London, 1944]]
On 16 June 1944 British double agent ''Garbo'' ([[Juan Pujol García|Juan Pujol]]) was requested by his German controllers to give information on the sites and times of V-1 impacts, with similar requests made to the other German agents in Britain, ''Brutus'' ([[Roman Czerniawski]]) and ''Tate'' ([[Wulf Schmidt]]). If the Germans had been supplied these data, they would have been able to adjust their aim and correct any shortfall. However, the double agents would  have been endangered because there was no plausible reason why they could not supply accurate data; the impacts would be common knowledge amongst Londoners and very likely reported in the press, which the Germans had ready access to through the neutral nations. As [[John Cecil Masterman]], chairman of the [[Twenty Committee]], commented, "If, for example, St Paul's Cathedral were hit, it was useless and harmful to report that the bomb had descended upon a cinema in [[Islington]], since the truth would inevitably get through to Germany ..."{{sfn|Masterman|1972|pp=252–53}}

While the British decided how to react, Pujol played for time. On 18 June it was decided that the double agents would report the damage caused by V-1s fairly accurately and minimise the effect they had on civilian morale. It was also decided that Pujol should avoid giving the times of impacts and should mostly report on those which occurred in the northwest of London, to give the impression to the Germans that they were overshooting the target area.{{sfn|Crowdy|2008|pp=273–74}}

While Pujol downplayed the extent of V-1 damage, trouble came from ''Ostro'', an {{lang|de|[[Abwehr]]}} agent in [[Lisbon]] who pretended to have agents reporting from London. He told the Germans that London had been devastated and had been mostly evacuated as a result of enormous casualties. The Germans could not perform aerial reconnaissance of London and believed his damage reports in preference to Pujol's. They thought that the Allies would make every effort to destroy the V-1 launch sites in France. They also accepted ''Ostro''{{'}}s impact reports. Due to [[Ultra (cryptography)|Ultra]], however, the Allies read his messages and adjusted for them.{{sfn|Masterman|1972|p=254}}

[[File:Bundesarchiv Bild 146-1981-004-19, Max Wachtel.jpg|thumb|upright|Max Wachtel]]
A certain number of the V-1s fired had been fitted with radio transmitters, which had clearly demonstrated a tendency for the V-1 to fall short. {{lang|de|[[Oberst]]}} Max Wachtel, commander of Flak Regiment 155 (W), which was responsible for the V-1 offensive, compared the data gathered by the transmitters with the reports obtained through the double agents. He concluded, when faced with the discrepancy between the two sets of data, that there must be a fault with the radio transmitters, as he had been assured that the agents were completely reliable. It was later calculated that if Wachtel had disregarded the agents' reports and relied on the radio data, he would have made the correct adjustments to the V-1's guidance, and casualties might have increased by 50 per cent or more.{{sfn|Jones|1978|p=422}}{{sfn|Crowdy|2008|p=280}}

The policy of diverting V-1 impacts away from central London was initially controversial. The War Cabinet refused to authorise a measure that would increase casualties in any area, even if it reduced casualties elsewhere by greater amounts. It was thought that [[Churchill]] would reverse this decision later (he was then away at a conference); but the delay in starting the reports to Germans might be fatal to the deception. So Sir [[Findlater Stewart]] of [[Home Defence Executive]] took responsibility for starting the deception programme immediately, and his action was approved by Churchill when he returned.{{sfn|Montagu|1978|pp=151–58}}