Despite being launched several days after "Hiyō", "Jun'yō" was the first of the pair to be commissioned in May 1942. She was assigned to the Fourth Carrier Division of the 1st Air Fleet, together with . The ship was tasked to support the invasion of the Aleutian Islands, an operation designed to coincide with the attack on Midway. "Jun'yō" carried 18 A6M2 Zeros and 18 D3As for this operation. The ship launched her first airstrike at dawn on 3 June against Dutch Harbor on Unalaska Island. She accomplished little during this operation, losing five aircraft to all causes, and her own aircraft only shot down five American aircraft.