Armed Forces Security Agency The National Security Agency ( NSA ) is the main producer and manager of signals intelligence ( SIGINT ) for the United States government . Estimated to be one of the largest of U . S . intelligence organizations in terms of personnel and budget , the NSA operates under the jurisdiction of the Department of Defense and reports to the Director of National Intelligence . The NSA is tasked with the global monitoring , collection , decoding , translation and analysis of information and data for foreign intelligence and counterintelligence purposes , including surveillance of targeted individuals in U . S . territory . The agency is authorized to accomplish its mission through clandestine means , among which are bugging electronic systems and allegedly engaging in sabotage through subversive software . The NSA is also responsible for the protection of U . S . government communications and information systems . As part of the growing practice of mass surveillance in the United States , the NSA collects and stores all phone records of all American citizens . Unlike the Defense Intelligence Agency ( DIA ) and the Central Intelligence Agency ( CIA ) , both of which specialize primarily in foreign human espionage , the NSA has no authority to conduct human - source intelligence gathering , although it is often portrayed doing so in popular culture . Instead , the NSA is entrusted with coordination and deconfliction of SIGINT components of otherwise non - SIGINT government organizations , which are prevented by law from engaging in such activities without the approval of the NSA via the Defense Secretary . As part of these streamlining responsibilities , the agency has a co - located organization called the Central Security Service ( CSS ) , which was created to facilitate cooperation between NSA and other U . S . military cryptanalysis components . Additionally , the NSA Director simultaneously serves as the Commander of the United States Cyber Command and as Chief of the Central Security Service . History . Army predecessor . The origins of the National Security Agency can be traced back to April 28 , 1917 , three weeks after the U . S . Congress declared war on Germany in World War I . A code and cipher decryption unit was established as the Cable and Telegraph Section which was also known as the " Cipher Bureau and Military Intelligence Branch , Section 8 " ( MI - 8 ) . It was headquartered in Washington , D . C . and was part of the war effort under the executive branch without direct Congressional authorization . During the course of the war it was relocated in the army ' s organizational chart several times . On July 5 , 1917 , Herbert O . Yardley was assigned to head the unit . At that point , the unit consisted of Yardley and two civilian clerks . It absorbed the navy ' s cryptoanalysis functions in July 1918 . World War I ended on November 11 , 1918 , and MI - 8 moved to New York City on May 20 , 1919 , where it continued intelligence activities as the Code Compilation Company under the direction of Yardley . Black Chamber . MI - 8 was also called the Black Chamber . Headed by cryptologist Herbert Yardley , the Black Chamber was located on East 37th Street in Manhattan . Its purpose was to crack the communications codes of foreign governments . Jointly supported by the State Department and the War Department , the chamber persuaded Western Union , the largest U . S . telegram company , to allow government officials to monitor private communications passing through the company ’ s wires . Other so called Black Chambers were also found in Europe . They were established by the French and British governments to read the letters of targeted individuals , employing a variety of techniques to surreptitiously open , copy , and reseal correspondence before forwarding it to unsuspecting recipients . Despite the American Black Chamber ' s initial successes , it was shut down in 1929 by U . S . Secretary of State Henry L . Stimson , who defended his decision by stating that , " Gentlemen do not read each other ' s mail " . World War II and its aftermath . During World War II , the Signal Security Agency ( SSA ) was created to intercept and decipher the communications of the Axis powers . When the war ended , the SSA was reorganized as the Army Security Agency ( ASA ) , and it was placed under the leadership of the Director of Military Intelligence . On May 20 , 1949 , all cryptologic activities were centralized under a national organization called the Armed Forces Security Agency ( AFSA ) . This organization was originally established within the U . S . Department of Defense under the command of the Joint Chiefs of Staff . The AFSA was tasked to direct Department of Defense communications and electronic intelligence activities , except those of U . S . military intelligence units . However , the AFSA was unable to centralize communications intelligence and failed to coordinate with civilian agencies that shared its interests such as the Department of State , Central Intelligence Agency ( CIA ) and the Federal Bureau of Investigation ( FBI ) . In December 1951 , President Harry S . Truman ordered a panel to investigate how AFSA had failed to achieve its goals . The results of the investigation led to improvements and its redesignation as the National Security Agency . The agency was formally established by Truman in a memorandum of October 24 , 1952 , that revised National Security Council Intelligence Directive ( NSCID ) 9 . Since President Truman ' s memo was a classified document , the existence of the NSA was not known to the public at that time . Due to its ultra - secrecy the U . S . intelligence community referred to the NSA as " No Such Agency " .