While "I-6" was at Yokosuka, the Aleutian Islands campaign began on 3–4 June 1942 with a Japanese air raid on Dutch Harbor, Alaska, followed quickly by the unopposed Japanese occupation in the Aleutian Islands of Attu on 5 June and Kiska on 7 June 1942. On 10 June 1942, "I-1", "I-2", "I-3", "I-4", "I-5", "I-6", and "I-7" were reassigned to the Northern Force for duty in the Aleutians, and on either 17 or 20 June 1942 "I-6" set out for Aleutian waters to begin her fourth war patrol. She joined the "K" patrol line in the Unimak Pass area. On 7 July 1942, she received orders to move to the Kiska area. When the rest of Submarine Squadron was ordered to return to Japan on 20 July 1942, she was ordered to remain behind and operate from Kiska.