Cryptography 17 History 16 World War, 1939-1945 8 Espionage, Soviet 6 Intelligence service 4 Diplomatic relations 3 Foreign relations 3 Security measures 3 Access control 2 American 2 Communication systems 2 Computer networks 2 Computers 2 Electronic intelligence 2 Enigma cipher system 2 Information networks 2 Korean War, 1950-1953 2 Military intelligence 2 Military operations, Naval 2 Naval operations, American 2 Telecommunication systems 2 African Americans in the civil service 1 Campaigns 1 Communications 1 Coral Sea, Battle of the, 1942 1 Cuban Missile Crisis, 1962 1 Digital communications 1 Drug abuse 1 Indochinese War, 1946-1954 1 Information technology 1