Alpha-Nine was originally a squad of ODSTs during the Human-Covenant war, consisting of various ODSTs and Spartans, though it most well-known for the following members:
Alpha-Nine fought in several battles towards the end of the war between 2546 and 2552. After the war, the squad was tasked with fighting a resurgence of insurrectionist activities, though these missions resulted in the early retirement of Dutch and the death of The Rookie. Soon after these losses, the remaining members of Alpha-Nine were recruited into the Spartan-IV program, joining into the second recruiting class in 2554. Buck, Mickey, and Romeo remained as Alpha-Nine after completing Spartan training, again fighting insurrectionists, but this time doing so in MJOLNIR.
Alpha-Nine was betrayed by Mickey in 2555 during Operation: COALPEPPER, who held insurrection sympathies. The team split up at this point, and Buck became a member of Fireteam Osiris. Buck remained on Osiris until after the Raising of the Guardians in 2558, when he was tasked with taking command of Alpha-Nine again, including bringing Mickey back from his imprisonment. During this mission it was discovered that Dutch had come out of retirement and was part of a new class of Spartan-IV recruits, and joined Alpha-Nine, making the squad a four-man team again.