On 21–22 April, she conducted training underway and was declared ready for sea on 25 April. "Wahoo" began her fifth war patrol on 25 April, departing Midway under air escort for patrol areas via the Kuril Islands. The following day, she patrolled the surface and reconnoitered Matsuwa, taking photographs of the enemy installations, exploring southwest along the island chain and finding the islands barren and completely covered with snow and ice. On 4 May, "Wahoo" proceeded to reconnoiter the northeast tip of Etorofu Island; she found nothing and changed course to the southeast. Morton positioned the boat to intercept the seaplane tender . The submarine submerged and fired a spread of three torpedoes. The first hit between the stack and bridge; the other two missed. "Kamikawa" turned away and was making , with a slight list. ("Kamikawa" survived but was sunk 29 May 1943 by the .) "Wahoo" continued on an easterly course, surfaced and continued her patrol of the Kurils southward. Three days later, "Wahoo" sighted two ships hugging the shoreline on a northerly course, off the Benten Saki coast, and dove. She launched two torpedoes at the leading ship, followed immediately by a spread of four at the escort. The first torpedo hit the leading ship, "Tamon Maru #5", under the stack and broke her back; the second missed ahead. The escort successfully avoided all four torpedoes fired at her and then escaped. The "Tamon Maru" () sank, and "Wahoo" proceeded down the coast. The submarine submerged off Kobe Zaki and sighted a three-ship convoy consisting of two escort vessels and a large naval auxiliary. "Wahoo" fired a spread of three torpedoes; two exploded prematurely, the third failed to explode. This ship got away, and "Wahoo" was forced down by the escorts. On the night of 9 May 1943, "Wahoo" proceeded up the coast with the intention of closing Kone Saki. Radar picked up two targets, soon identified as a large tanker and a freighter in column, evidently making the night run between ports without an escort. The submarine fired a spread of three torpedoes at the tanker and immediately thereafter a three torpedo spread at the freighter. "Wahoo" had two successful hits, and both ships went down; "Takao Maru" () and "Jinmu Maru" ().