MI6 has lifted the lid on their secretive operations in the first approved book.
The author, professor Keith Jeffery from Queen's University in Belfast was given unrestricted access to the surviving historic files of the Secret Intelligence Service (SIS).
The book was launched at the Foreign office where Sir John Scarlett, the former SIS chief said it was a "radical step" for the covert agency.
He commissioned the book to mark its centenary last year: "Mansfield Cumming (the first service's first chief) believed passionately in secrecy. I am sure he would be surprised to see me here today presenting a history of his service.
"For MI6, this is an exceptional event. There has been nothing like this before and there are no plans for anything similar in the future," Sir John said.
He continued: "Although for much of its history it was astonishingly underfunded and very much smaller than imagination would have it, the overall impression one is left with is the remarkable level of achievement against a very wide range of extremely difficult and stressful intelligence targets on five continents."
Unlike the recent authorised history of MI5, which runs to the present day, it only covers the first 40 years of the service from 1909 to 1949.
Prof Jeffery also had to agree to a number of restrictions on what he could write, including a promise that he would not name or allude to any agent whose identity was not already clearly in the public domain.