You are correct. The peacekeeper needed it because of the mobile basing requirement. Most missiles would sit in a static silo, with the INS having a contant reference that doesn't move. Mobile basing required the need for a better INS system. AIRS is being moved to the Minuteman III for reasons I'm not quite sure, other than they had 50 of them for the MX program, now they built another 600 or so for the entire Minuteman program. Government welfare for the defense industries?