Fifth patrol, April ? May 1943
Wahoo began her fifth war patrol on 25 April, departing Midway under air escort for patrol areas via the Kurils. 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 a seaplane tender, Kamikawa Maru. 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 11 knots (20 km/h), with a slight list. (Kamikawa survived but was sunk May 29, 1943 by Scamp.) 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, 12 nautical miles (22 km) off the Benten Saki coast, and dived. 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 escaped. Tamon Maru (5,260 tons) sank, and Wahoo proceeded down the coast.
The submarine submerged 1 nautical mile (1.9 km) 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, 3,200 tons and Jinmu Maru, 1,200 tons.
Wahoo cleared the area to the northeast in order to patrol the Tokyo-Paramushiro route; on 12 May, she sighted two freighters. She dove to gain position for a "two ship" shot where they would come by in column. She launched four torpedoes from 1,200 yards (1,100 m), but got only one hit. Morton fired his last two torpedoes. Nothing was seen of the first. The second hit under the bridge with a dull thud, much louder than the duds heard only on sonar but lacking the "whacking" noise which accompanies a wholehearted explosion. The other freighter opened fire with heavy guns and charged Wahoo. Both ships got away. Wahoo cleared the area to the east and set course for Pearl Harbor.
Wahoo's fifth war patrol was again considered outstanding in aggressiveness and efficiency. In ten action-packed days Wahoo delivered ten torpedo attacks on eight different targets. However, faulty torpedo performance cut positive results by as much as one-half.
In these last three patrols, Wahoo established a record not only in damage inflicted on the enemy for three successive patrols, but also for accomplishing this feat in the shortest time on patrol: a total of 93,281 tons sunk and 30,880 damaged in only 25 patrol days.
Wahoo arrived at Pearl Harbor on 21 May 1943. The next day, Admiral Chester W. Nimitz, Commander in Chief, U.S. Pacific Fleet, came on board and made presentations of awards. Two days later, the submarine departed for the Mare Island Navy Yard, where she arrived 29 May to commence overhaul. From 11 ? 20 July the submarine underwent intensive post-repair trials and training. On 20 July, squadron commander Captain John B. Griggs, Jr., came aboard and presented more awards. The following day, Wahoo departed for Pearl Harbor, furnishing services for surface and air forces while en route. She arrived at Hawaii on 27 July 1943 and departed on 2 August for her patrol area. Four days later, Wahoo arrived at Midway Island but left the same day.