SB Media on Instagram: "On September 19, 1957, the United States conducted “Rainer”, the first fully contained underground nuclear test, as part of Operation Plumbbob at the Nevada Test Site. With a yield of 1.7 kilotons, it was small by nuclear standards, but massive in impact. Unlike earlier atmospheric tests, Rainer was detonated in a horizontal tunnel deep underground. The goal: to test whether nuclear blasts could be fully contained without releasing radioactive fallout into the environment