Mirrin Prime was a planet in the Mirrin sector, which was controlled by the New Republic during the Cold war. It hosted a New Republic military base which included Rapier Squadron, a four-member T-85 X-wing squadron that was part of the New Republic Defense Fleet. The base's commanding officer was Major Lonno Deso. Space traffic was monitored by Mirrin Control and Mirrin Flight.
After Rapier Squadron's commander Poe Dameron participated in an unauthorized mission to rescue the Yissira Zyde, the Squadron left Mirrin Prime to join the Resistance, a private military group led by General Leia Organa which opposed the First Order. Rapier Squadron was transferred to the Resistance's refitted Mon Calamari cruiser Echo of Hope.