Gaelin-A271 was the sniper and marksman SPARTAN-III of Centurion Team, who were most known for their involvement in the Conflict of New Zaječar, which took place on the industrial colony of New Zaječar. Centruon Team consisted of SPARTAN-IIIs Vincent-A271, Ivana-A373 and Boško-A153. They were assisted by two of the now legendary SPARTAN-II's, known as Doug-103 and Colin-142.