British codebreaker’s memoir of WWII, where he tried to keep agents safe and occasionally succeeded. Dry British humor and lots of bureaucratic infighting.

Reading various spy/intelligence memoirs, it often appears that for intel types, the enemy is not so much their opposite numbers on the other side, but other intelligence agencies/departments on their own side (because of turf wars, mostly, but also frequently a strong conviction that the other agency/department is Getting Everything Wrong.)