And here is a 32-minute formerly secret official documentary (with English subtitles) prepared for Soviet leader Joseph Stalin about the extensive preparations for and execution of that first atomic weapon test, along with a detailed report about the results.

Radioactive debris from this test was detected in early September by US Air Force WB-29 reconnaissance aircraft and a US Navy program to collect and analyze fallout in rainwater. Once traced back to its source—see next link for how that happened—President Truman announced the test on September 23.

[Source: “Finding the Site of the First Soviet Nuclear Test in 1949,” by former U.S. Weather Bureau meteorologist Lester Machta in the Bulletin of the American Meteorological Society (1992)]. journals.ametsoc.org/view/journal...

President Truman was initially not certain he wanted to publicly announce the Soviet nuclear test, worrying that doing so would have serious diplomatic and economic repercussions. When he finally did, however, he did not say it was an atomic bomb test, only that “an atomic explosion occurred.”

Today is also the 34th anniversary of the closure of the Semipalatinsk Test Site—aka the Polygon—and the 16th International Day Against Nuclear Tests, established by the United Nations in 2009 at the urging of Kazakhstan and other states to commemorate that milestone.