One of the best-known children's authors of last century was suspected of being a spy by British intelligence.
Children's author Arthur Ransome
Arthur Ransome wrote the book Swallows and Amazons in 1930, but also worked in the Soviet Union (which Russia used to be a part of) for British newspapers.
While there British spy bosses used him to send them information, but were worried he worked for the Soviets too.
They later decided that Ransome was loyal to Britain, but was very interested in the Soviet way of life.
Files about security issues are often sealed to stop people learning secrets they may contain, which is why these documents have only just been made available to the public.
The released documents also include tips given to Soviet agents working in London in the 1930s, including where to live and good places to meet other agents.
There was also information on the amazing devices used during WWII and how they may have inspired some of the gadgets used by James Bond.
The author of those books, Sir Ian Fleming, worked for the Navy during the war and may have got the idea for human torpedoes used in Thunderball from techniques used by Italy during that time.