When the Indo-Pakistani War broke out in 1965, Sareen was with No.29 Scorpios Squadron flying the Ouragans at Gauhati. He undertook some sorties against targets in East Pakistan, but the fighting was minimal in the Eastern Sector. After the war, Sareen moved to No.27 Flaming Arrows Squadron flying the Hawker Hunter. After a brief stint, he was part of a detachment of pilots earmarked for conversion to MiG-21s. Sareen moved back to No.29 Squadron after it converted back to the MiG-21.