The August 1939 Hitler-Stalin non-aggression pact drove Chambers to take action against the Soviet Union. In September 1939, at the urging of anti-Communist, Russian-born journalist Isaac Don Levine, Chambers and Levine met with Assistant Secretary of State Adolf A. Berle. Levine had introduced Chambers to Walter Krivitsky, who was already informing American and British authorities about Soviet agents who held posts in both governments. Krivitsky told Chambers it was their duty to inform. Chambers agreed to reveal what he knew on the condition of immunity from prosecution. During the meeting, which took place at Berle's home, Woodley Mansion in Washington, Chambers named 18 current and former government employees as spies or Communist sympathizers. Many names mentioned held relatively minor posts or were already under suspicion. Some names, however, were more significant and surprising: Alger Hiss, his brother Donald Hiss, and Laurence Duggan--who were all respected, mid-level officials in the State Department--and Lauchlin Currie, a special assistant to Franklin Roosevelt. Another person named had worked on a top secret bombsight project at the Aberdeen Proving Grounds. Berle found Chambers' information tentative, unclear, and uncorroborated. He took the information to the White House, but the President dismissed it, to which Berle made little if any objection. Berle kept his notes, however (later, evidence during Hiss' perjury trials). Berle notified the Federal Bureau of Investigation (FBI) of Chambers's information in March 1940. In February 1941, Krivitsky was found dead in his hotel room. While police ruled the death a suicide, it was widely speculated that Krivitsky had been killed by Soviet intelligence. Worried that the Soviets might try to kill Chambers too, Berle again told the FBI about his interview with Chambers. Nevertheless, the FBI took no immediate action, in line with the political orientation of the United States, which viewed the potential threat from the USSR as minor, when compared to that of Nazi Germany. (The FBI did interview Chambers in May 1942 and June 1945, without further action. Only in November 1945, when Elizabeth Bentley defected and corroborated much of Chambers's story, did the FBI begin to take Chambers seriously).

Answer this question "When did this meeting occur?" by extracting the answer from the text above.
In September 1939,