moved toward the Kuril Islands for her first war patrol. On 21 and 22 April, snow and fog covered her approach to Paramushiro and Onekotan Strait. On 23 April, she sighted and was sighted by, a large enemy submarine on the surface. Both submarines submerged. Explosions were felt in S-35. The blasts forced her down further than expected, but she regained control at 220 feet, returned to her intended depth; and maneuvered out of the immediate area. The weather cleared on 24 April, and Paramushiro was sighted for the first time. Two days later, however, the S-boat was en route to her secondary station north of Attu. On arrival on 27 April, a ship's cook was discovered to have mumps and a course was set for Dutch Harbor. Isolation was impossible, and half the crew had not had the disease. Three days later, S-35 returned to her Unalaska base. The crew received medical attention, the boat was scrubbed down and refitted; and requests for modern equipment, including sonar and radar, were made. Second war patrol Toward the end of May, the submarine was ready for sea; and, on 28 April, she moved west in response to intelligence reports of a Japanese invasion force bound for the western Aleutian Islands. On station by 30 April, she patrolled on the surface with no contacts, through 2 June. On the morning of 3 June, word of the bombing of Dutch Harbor was received. Aerial contacts, both friendly and enemy became frequent; but the submarine was not attacked. On 11 June, she was ordered back to Dutch Harbor to replenish; thence, she was routed to the western part of the archipelago for offensive operations near Kiska which had been taken by the Japanese. On 14 June, she approached the island and patrolled between there and Segula until 23 June. She then participated in the search for sister ship , which had run aground on Amchitka Island; returned to her patrol area late on 25 June; and, on 29 June, returned to Dutch Harbor. The thick fog which had shielded the Japanese force as it crossed the Bering Sea had remained over the Aleutians during her patrol, impairing visibility and hindering her offensive efforts. Third war patrol On 14 July, S-35 got underway again and, through the end of the month, patrolled the Japanese supply lanes to Kiska. She then headed back toward Dutch Harbor,