Soviet intelligence defector Walter Krivitsky has the first of several debriefings at the Department of State.
President Roosevelt secretly gives the Federal Bureau of Investigation (FBI), the Military Intelligence Division (MID), and the Office of Naval Intelligence (ONI) exclusive responsibility for counterespionage.
Germany and USSR sign Non-Aggression Pact.
World War II begins as Germany invades Poland.
President Roosevelt authorizes the FBI to conduct warrantless electronic surveillance of persons suspected of subversion or espionage; surveillance was to be limited insofar as possible to aliens.
FBI-MID-ONI "Delimitation Agreement" further specifies the division of labor in domestic intelligence work.
The Alien Registration Act (the "Smith Act") criminalizes conspiracy to overthrow the government, requires resident aliens to register, report annually, and provide notice of address changes.
KGB agent Ramon Mercader assassinates Leon Trotsky in Mexico.
Walter Krivitsky found dead of a gunshot wound in a Washington hotel; the police rule his death a suicide.
Federal agents arrest Amtorg employee and KGB New York rezident Gaik Ovakimian for violating the Foreign Agents Registration Act.
Germany invades Russia.
FBI arrests 29 German military intelligence agents, crippling Germany's clandestine operations in the United States.
US Government allows Ovakimian to leave the country.
London KGB rezident Anatoli Gorski informs Moscow that his agent reports London has decided to build an atomic bomb.
Japanese aircraft attack Pearl Harbor; America enters the war.
Senior KGB officer Vassili M. Zarubin arrives in San Francisco on his way to succeed Ovakimian as New York rezident.
MID's Special Branch begins producing daily "Magic Summaries" analyzing foreign diplomatic messages for the White House and senior military commanders.
The Office of the Coordinator of Information becomes the Office of Strategic Services (OSS), subordinate to the Joint Chiefs of Staff.
Interagency agreement divides signals intelligence duties: Navy assigned to handle naval codebreaking; the US Army's Signals Intelligence Service to handle diplomatic and military traffic; and the FBI works clandestine radio communications.
President Roosevelt bars all agencies except the FBI and the armed services from code-breaking activities. The services interpret this directive as authorization to deny signals intelligence to OSS.
US Army's renamed Signal Security Agency (SSA) formally begins work on Russian diplomatic traffic.
KGB New York rezident Vassili M. Zarubin meets CPUSA official Steve Nelson in Oakland and discusses espionage.
Communist International (Comintern) resolves to disband.
FBI receives an anonymous Russian letter naming Soviet intelligence officers in North America.
San Francisco KGB residency acknowledges the receipt of a new codebook.
The KGB, apparently on short notice, changes the indicator system for its cables, leaving the one-time pad page numbers en clair.
SSA's Cecil Phillips discovers the new KGB indicator, which is then used to detect "key" duplicated in Trade messages.
OSS purchases Soviet code and cipher material from Finnish sources; the Roosevelt administration orders the material returned to the Soviet Embassy in Washington.
The War Department transfers operational control of SSA from the Signal Corps to MID.
President Roosevelt dies; Harry Truman sworn in as his successor.
A US Army Target Intelligence Committee (TICOM) team finds Russian code and cipher material in a German Foreign Office cryptanalytic center in a castle in Saxony-Anhalt.
FBI conducts a lengthy debriefing of former Soviet agent Whittaker Chambers.
Earl Browder ousted as leader of the Communist Political Association, which reclaims its old name, the Communist Party of the United States (CPUSA).
The Manhattan Project detonates the world's first nuclear explosion, Trinity, in New Mexico; Soviet agents had warned Moscow in advance.
Soviet GRU code clerk Lt. Igor Gouzenko defects in Ottawa.
The War Department authorizes merger of SSA with selected Signal Corps units to form the Army Security Agency (ASA), under MID.
US-UK signals intelligence Continuation Agreement extends wartime cooperation in this field.
President Truman dissolves OSS.
Elizabeth Bentley interviewed at length for the first time by FBI agents about her work for the KGB.
Truman creates the Central Intelligence Group and the position of Director of Central Intelligence (DCI).
The State-Army-Navy Communications Intelligence Board adds the FBI and renames itself the United States Communications Intelligence Board (USCIB).
National Intelligence Authority Directive 5 secretly directs the DCI to conduct, as "services of common concern," all foreign intelligence and counterespionage.
CIG joins the new USCIB and gains access to signals intelligence.
A Canadian Royal commission releases its report on the Gouzenko affair to the public.
Attorney General Tom Clark urges Truman to renew and broaden Roosevelt's 1940 authorization to conduct electronic surveillance on "persons suspected of subversive activities"; the President soon approves.
ASA's Meredith Gardner translates part of a KGB message containing a list of atomic scientists.
Executive Order 9835 tightens protections against subversive infiltration of the US Government, defining disloyalty as membership on a list of subversive organizations maintained by the Attorney General.
President Truman signs the National Security Act of 1947, creating the National Security Council (NSC) and transforming CIG into the Central Intelligence Agency (CIA).
Around 1 September
Col. Carter Clarke briefs the FBI's liaison officer on the break into Soviet diplomatic traffic.
NSCID-5 reiterates but qualifies DCI's counterespionage authority to avoid precluding certain "agreed" FBI and military counterintelligence activities.
NSCID-9 puts USCIB under the NSC and increases civilian control of signals intelligence.
General Secretary Eugene Dennis and 11 other CPUSA leaders arrested and indicted under the Smith Act of conspiring to advocate violent overthrow of the US Government.
Elizabeth Bentley testifies before the House Committee on Un-American Activities (HCUA), publicly accusing Harry Dexter White and Lauchlin Currie of being Soviet agents.
Whittaker Chambers names Alger Hiss and Harry Dexter White as Communists in testimony before the HCUA.
Meredith Gardner and Robert Lamphere meet at Arlington Hall and formally inaugurate full-time FBI-ASA liaison on the Soviet messages.
Chambers produces the "Pumpkin Papers" to substantiate his new charge that Hiss and White spied for Moscow during the 1930s.
A federal grand jury indicts Alger Hiss for perjury.
FBI identifies covername SIMA as Justice Department analyst Judith Coplon.
FBI arrests Coplon and Soviet UN employee Valentin A. Gubitchev in New York.
Truman approves NSC 17/4, which reconstitutes the secret Interdepartmental Intelligence Conference to coordinate jurisdiction of FBI and military counterintelligence.
Defense Secretary Louis Johnson directs a quasi-merger of service signals intelligence in a new Armed Forces Security Agency (AFSA), subordinate to the JCS.
Truman announces that the Soviets have exploded an atomic bomb.
The People's Republic of China is proclaimed in Beijing.
Alger Hiss is convicted of perjury.
Klaus Fuchs confesses to espionage.
Senator Joseph R. McCarthy, in a speech in Wheeling, West Virginia, brandishes a list of Communists allegedly working in the State Department.
FBI arrests Harry Gold for espionage.
North Korean troops invade South Korea.
FBI arrests Julius Rosenberg.
AFSA assigns Soviet intercept material a restricted codeword ("Bride") and special handling procedures.
Congress passes the Internal Security Act (the "McCarran Act"), which it would soon pass again over President Truman's veto. The Act requires Communist-linked organizations to register and allows emergency detention of potentially dangerous persons.
British Foreign Office officials Donald Maclean and Guy Burgess flee Great Britain to defect to the Soviet Union.
CPUSA announces that the Party will operate as a "cadre organization," with many of its leaders underground.
AFSA detects duplicate key pages in GRU messages.
Truman creates the National Security Agency (NSA) to supersede AFSA and further centralize control of signals intelligence under the Secretary of Defense and a reconstituted USCIB.
NSA places the "POBJEDA" codebook--recovered in Germany in April 1945--against KGB messages from 1941 through 1943. More than half of the burned codebook proves useable.
KGB defector Alexander Orlov's story appears in Life magazine; finally alerting the FBI to his residence in the United States.
Julius and Ethel Rosenberg executed after President Eisenhower again denies executive clemency.
Armistice signed in Korea.
Attorney General Herbert Brownell sparks controversy by claiming in a Chicago speech that former President Truman had appointed Harry Dexter White to head the International Monetary Fund despite FBI warnings that White was a Soviet agent.
CIA's Directorate of Plans creates the Counterintelligence Staff, with James J. Angleton as its chief.
NSC approves the FBI's proposed "Cointelpro" operation against the CPUSA.
The Department of State releases Soviet General Secretary Khrushchev's secret speech to the Twentieth Party Congress, in which Khrushchev denounced Stalin's crimes.
Soviet troops suppress a popular uprising in Hungary.
FBI arrests Jack and Myra Soble for espionage on the basis of evidence provided by double agent Boris Morros.
KGB officer Reino Hayhanen, en route from the United States, defects at the US Embassy in Paris.
Supreme Court in Yates v. US rules the government had enforced the Smith Act too broadly by targeting protected speech instead of actual action to overthrow the political system; this ruling makes the Act almost useless for prosecuting Communists.
Federal authorities detain Hayhanen's superior, KGB illegal Col. Rudolf Abel, in New York.
Abel is sentenced to 30 years and conveyed to prison.