AN602: Tsar Bomba
The Soviet Union detonates the most powerful thermonuclear weapon built to date, code-named AN602, or, more informally, “Tsar Bomba”. Though it’s designed to deliver a yield of 100 megatons, the 27-ton device is only fueled enough to produce a 50-megaton explosion, still enough to be detected by other nations. (A U.S. reconnaissance aircraft is close enough to witness the detonation, so the test is hardly a secret to the western world.) The detonation registers on seismic sensors, and interferes with radio transmissions nearby for nearly an hour; the explosion is visible as far away as Norway and Alaska. Due to modifications made to avoid endangering the Soviet population, fallout is minimal, though that might not be the case were the weapon to be deployed offensively.