Sarah Palmer was born on Luna, the human colony located on Earth's moon in 2527. Once she was of enlistment age, she joined the Orbital Drop Shock Troopers and was a part of twelve tours of duty during the war. Afterwards, she was one of the first people approached to be part of the Spartan-IV program, and joined the first class of Spartan-IVs. Palmer was involved in many tours as a spartan, rising to commander of the Spartan Branch aboard the UNSC Infinity. She led many operations as commander, including Operation: ATHENA which saw the final conflict over the Janus Key and Absolute Record. Soon after she was at the Battle of Sunaion, supporting Jameson Locke and Fireteam Osiris' efforts to track down Spartan-II Blue Team during the Raising of the Guardians.