POWs are considered held by factions, not individual players. Opposing faction leaders may agree to conduct the Prisoner Exchange mission in place of one of their attacks. Pilot POWs may also elect to use XP in an attempt to escape. If either faction holds a unique pilot POW, the other faction may choose to perform the Prisoner Rescue scenario in place of one of their attacks.
A player whose Squadron commander is POW may elect to purchase a new Squadron commander after being without a commander for a minimum of one battle phase. If they do so, their original commander is considered shipped off to a secure detention facility and is no longer able to be rescued.