From Halopedia, the Halo wiki
Recruit is an achievement in Halo: Spartan Assault. It is unlocked by earning a star of any type in an operation mission. The achievement is worth 5 Gamerscore on Xbox 360 and Windows systems, and 10 Gamerscore on Xbox One. It is represented by a circle with a star.
If previously unlocked on another device, this achievement will unlock on the Xbox One the first time the player signs in. On the other platforms, it will unlock when the player earns their first medal.