Secret service History 76 World War, 1939-1945 70 Spies 24 Intelligence service 22 Military intelligence 19 Underground movements 11 more ... Campaigns 9 Espionage 8 Cold War 7 Cryptography 5 Intelligence officers 5 Subversive activities 5 Electronic intelligence 4 Espionage, British 4 Naval operations, British 4 Officers 4 Participation, Female 4 Politics and government 4 Women spies 4 Deception 3 Espionage, German 3 Foreign relations 3 Internal security 3 Prisoners of war 3 Soldiers 3 World War, 1914-1918 3 Collaborationists 2 Commando operations 2 Escapes 2 less ...