CIA Studies in Intelligence – https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/csi-studies/index.html
Representative questions that can be answered with this resource:
- Where can I learn about Soviet defectors from Gorbachev’s Russia?
- Where I can learn more about the Chinese intelligence services?
- What did Ernest Hemmingway do for American intelligence during World War II?
- How do CIA staff go about determining a state’s instability?
Declassifed articles on a wide range of current and historical intelligence topics. Articles from 2011 included:
- The Evolution of US Army HUMINT: Intelligence Operations in the Korean War by John P. Finnegan
- Cultural Topography: A New Research Tool for Intelligence Analysis by Jeannie Johnson and Matthew Berrett
- What I Learned in 40 Years of Doing Intelligence Analysis for US Foreign Policymakers by Martin Petersen
May be useful in building characters or back story. According to the CIA page on copyright, you ought to be able to use quotes from the articles without copyright worries:
Unless a copyright is indicated, information on the Central Intelligence Agency Web site is in the public domain and may be reproduced, published or otherwise used without the Central Intelligence Agency’s permission. We request only that the Central Intelligence Agency be cited as the source of the information and that any photo credits or bylines be similarly credited to the photographer or author or Central Intelligence Agency, as appropriate.
If a copyright is indicated on a photo, graphic, or any other material, permission to copy these materials must be obtained from the original source.
Some of Mr. Petersen’s material sounded like it could be useful in the mouth of a veteran intelligence operative explaining the facts of life to a new colleague.