Sixth patrol, August 1943
On 13 August, Wahoo entered the Sea of Okhotsk, having completed passage through the Etorofu Strait. She arrived in the Sea of Japan the following day and sighted three medium freighters headed south. The submarine launched one torpedo at the trailing ship; it missed. The next day (15 August), while still on the trail of those three freighters, Wahoo sighted a large freighter on a northerly course. Deciding to attack the larger, single target, the submarine broke off the pursuit of the three freighters, surfaced, and commenced tracking the new target, diving to make a submerged approach. Wahoo launched one torpedo; it hit at the point of aim but was a dud. She fired two more torpedoes. Both missed. Wahoo then swung around to bring her stern torpedo tubes to bear and headed directly for the target. The submarine fired another torpedo which missed and must have broached and exploded before the end of the run. Wahoo soon sighted an Otori-class torpedo boat and commenced evasive action, letting the large freighter escape. She decided to move over on the Hokkaidô-Korea shipping route and spend the night and the following day transiting to that area.
On 16 August, Wahoo sighted a freighter headed south, but made another contact in a better position for attack. Shifting targets, she launched one torpedo at a medium-sized freighter. It missed. The next day, the scene was repeated with the same results. No pursuit was undertaken, in hopes of a loaded target heading south. However, Wahoo sighted a freighter heading north in ballast and commenced a submerged approach. Morton launched one torpedo which missed. Just as the torpedo left its tube, a southbound freighter passed close aboard this target, but the torpedo missed. Wahoo then surfaced and chased the southbound freighter. While pursuing this ship, the submarine sighted another target well ahead and away from the coast, so she again shifted targets. While tracking this new target, she passed two small northbound ships?one looked like a tug and the other resembled a tanker. Wahoo made a submerged approach and launched a torpedo at the medium-sized freighter. It was a miss. She fired again; still a miss, but this torpedo, probably broaching, exploded. The submarine surfaced and headed further out to sea.
Within four days, twelve Japanese vessels were sighted; nine were hunted down and attacked to no avail. Ten torpedoes broached, made erratic runs, or were duds. In light of the poor torpedo performance, ComSubPac ordered Wahoo to return to base.
On 19 August, the submarine sighted a ship and commenced tracking, but withheld fire when she recognized the flag as Soviet (an ally of the United States at the time). Wahoo made for La Perouse Strait. The next day, she sighted a sampan and fired warning shots across the bow. When the sampan failed to stop, the submarine opened up on it with her 20 millimeter and four-inch (102 mm) guns. The sampan was soon a wreck. Six Japanese fishermen surrendered and were taken on board as prisoners of war. Eight hours later, Wahoo opened fire on two more sampans, enveloping them in flames. Members of the crews jumped overboard but showed no desire to be rescued. Wahoo completed the passage of Etorofu Strait and arrived at Midway on 25 August. She immediately got underway for Pearl Harbor and arrived there on 29 August.