Division X was a short-lived, top secret department created by the CIA in 1962 to recruit mutants. It was run by The Man in Black, and was primarily stationed at the Covert CIA Research Base. It also formed the nucleus of the original X-Men team.
In 1962, Charles Xavier and Erik Lehnsherr were responsible for recruiting mutants found through Charles' use of Cerebro. Ultimately, in addition to already having Raven Darkholme and Hank McCoy, they were able to recruit Angel Salvadore, Armando Muñoz, Alex Summers, and Sean Cassidy. Logan was also considered as a potential recruit, but turned Xavier and Lehnsherr down.
Once gathered, Division X was stationed at the Covert CIA Research Base. They remained there until the Hellfire Club destroyed the facility, recruited Angel, and killed Darwin and the Man in Black. After these events, the remaining team mates regrouped under Xavier at the X-Mansion and he began to formally train them to hone their abilities so they could defeat the Shaw and his team in Cuba.