Britain compiled considerable documentation on what it believed to be Japanese wartime intelligence organizations along with some postwar concerns in the 1950s about the re-emergence of spying, files released to the public Friday revealed.
The files, now at the National Archives in London, span from 1936 to the end of 1954 and serialize the "top secret" information garnered on Japan's spying missions, both on British territory and across the world.
A document contained near the beginning of the records, dated November 1937 and titled "General Survey of the Japanese Espionage Services," tracks the broader movements of the Japanese secret services, with a particular focus on activities in the former Soviet Union, which are described as being "highly developed."