January 31.
On this day, 1950, US President Harry S. Truman announces the US's intention to build a hydrogen bomb.
Non-military -- on this day, 1961, Ham the Chimp, the first hominid to be launched into outer space. Surprisingly, this was not a one way mission, and Ham lived until 1983, until the ripe old age of 26 (he was only 2 at the time of his mission), having spent years at the National Zoo in Washington DC and then the North Carolina Zoo.
