the UK’s intelligence, security and cyber agency

From its origins in WW1, through to WW2 and the crucial contribution of Bletchley Park, GCHQ’s web site gives fascinating details of the organisations history.

https://www.gchq.gov.uk/section/history/our-origins-and-wwi

https://www.gchq.gov.uk/section/history/bletchley-park-and-wwii