During the
Second World War, in February 1940, then at the rank of Major, he transferred to the
Royal Artillery from the Yeomanry. As Lieutenant Colonel, Fleetwood-Hesketh was a member of
Ops (B), the deception section of SHAEF that helped plan
Operation Fortitude, a key portion of
Operation Bodyguard, the deception plan covering the Allied invasion of Normandy in 1944. He wrote a history of his role and the operation that was published after his death. Following the end of the war, Hesketh was sent to Germany, alongside his brother, to search through the files of German intelligence, and question officers. He was then asked to write a history of deception in Western Europe, including the work up to and including Operation Fortitude. In the 1970s books about Second World War deception began to appear.
Sefton Delmer's 1971 book,
The Counterfeit Spy, appeared to be copied from Hesketh's earlier unpublished report.
Noel Wild had provided Delmer with a copy of the report. Hesketh was annoyed and threatened to sue. However, the Government claimed
Crown Copyright on his report and he was not able to. In the end Delmer added a credit to the second edition of the book, and Hesketh and other deceivers were able to correct inaccuracies. Hesketh's report was eventually published posthumously in 1999, with a foreword by "Nigel West" (the pseudonym of
Rupert Allason). ==Political career==