Question: When did the project Operation Big was related to begin?

Context paragraphs:
Operation Big Switch: Operation Big Switch was the repatriation of all remaining prisoners of the Korean War.  Ceasefire talks had been going on between Communist and UN forces since 1951, with one of the main stumbling blocks being the Communist insistence that all prisoners be returned home, with the UN insisting that prisoners who wished to remain where they were be allowed to do so.  After talks dragged on for two years, the Chinese and North Koreans relented on this point, and the Korean Armistice Agreement was signed on July 27, 1953.

Operation Epsilon: Operation Epsilon was the codename of a program in which Allied forces near the end of World War II detained ten German scientists who were thought to have worked on Nazi Germany's nuclear program.  The scientists were captured between May 1 and June 30, 1945, as part of the Allied Alsos Mission, mainly as part of its Operation Big sweep through southwestern Germany.

Operation Big Ben: Operation Big Ben was the title given to the dive-bombing British Spitfire missions against German mobile V-2 rocket launch sites in Holland between October 1944 - April 1945, during World War II.  The code word 'Big Ben' meant 'V2 Rocket' and was used by the Filter Room at Fighter Command and by the pilots of the mission; but the phrase 'Operation Big Ben' was not used in official documentation (none found since the release of former Top Secret papers from the National Archive from January 2004), even though pilots (such as Flt Lt Raymond Baxter, who went on to become the voice of the Farnborough Air Show and BBC TV's technology programme Tomorrow's World) identified the sorties under the name 'Operation Big Ben'.

Operation Big Bird: "Operation Big Bird" (Filipino: "Oplan Big Bird") was the attempt of the Philippine Government during the presidency of Corazon Aquino to recover the alleged US$7.5 billion of hidden accounts and assets of President Ferdinand Marcos and his family in the Swiss banks.  Conceived by Philippine banker Michael de Guzman, it commenced shortly after Marcos was forced into asylum in the United States.  Initially, Operation Big Bird did not recover any money with two differing reports by Representative Victorio Chaves and Senator Jovito Salonga.  Chaves laid the blame upon Salonga, Solicitor-General Sedfrey Ordoñez and the Swiss bank lawyers.  Salonga countered that Ordoñez had prevented the Philippine government from losing a large sum of money.  Evidence suggests that de Guzman acted in good faith on behalf of the new government but that a double cross may have been present.

1269th Engineer Combat Battalion (United States): The 1269th Engineer Combat Battalion was an Engineer Combat Battalion that served in the United States Army in the European Theater of Operations during World War II.  It saw action in France and Germany, serving notably with the Army's T-Force intelligence assault force in the capture of German atomic weapons facilities and personnel as part of Operation Big.

Operation Big: Operation Big was an operation of the Alsos Mission, the Allied seizure of facilities, materiel, and personnel related to the German nuclear weapon project during World War II.  It was tasked with sweeping several targeted towns in the area of southwest Germany designated to the French First Army, including Hechingen, Bisingen, Haigerloch, and Tailfingen.

Operation Big Coon Dog: Operation Big Coon Dog was an investigation by the United States Federal Bureau of Investigation (FBI) and the Internal Revenue Service (IRS) into alleged corruption surrounding the use of federal and state disaster recovery funds by public officials in Buchanan County, Virginia, United States following severe flooding in the town of Hurley in May 2002.  The investigation resulted in the criminal conviction of sixteen people, including several public officials and other government employees, on charges of bribery and fraud.  It has been called the largest public corruption case in western Virginia in decades and a step towards uncovering a "dark culture of corruption in Buchanan County".

German nuclear weapon project: The German nuclear weapon project (German: "Uranprojekt" ; informally known as the "Uranverein"; English: Uranium Society or Uranium Club ) was a scientific effort led by Germany to develop and produce nuclear weapons during World War II.  The first effort started in April 1939, just months after the discovery of nuclear fission in December 1938, but ended only months later due to the German invasion of Poland, after many notable physicists were drafted into the "Wehrmacht".

Nikolajs Štelbaums: Nikolajs Štelbaums or Nikolay Shtelbaums (Russian: Николай Штельбаумс ) (13 October 1933 Užava parish, Latvia - 3 April 2008 Omsk, Russia) is a former Soviet speedskater.  As a child he was forced to move to Siberia along with his family in 1949, in connection with the Soviet mass deportation project Operation Priboi of more than 90,000 Estonians, Latvians and Lithuanians.  During his skating career he lived in Omsk, skating for Burevestnik.

Minuteman Mobility Test Train: A Minuteman Mobility Test Train was a Cold War train for Strategic Air Command testing before deployment of planned trains for launching Minuteman missiles which were to allow periodic movement for security from targeting by the Soviet missile force.  At the time, the trains had the heaviest railroad cars used on regular rail routes, and rail sidings were surveyed during the trains' 1960 Operation Big Star (surveyed sites were subsequently used in 1961 by different SAC trains for evaluating bomber accuracy.)

Supporting paragraphs: Operation Big German nuclear weapon project
Answer: April 1939