On 13 August, "Wahoo" entered the Sea of Okhotsk, having completed the 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 Hokkaidō-Korea shipping route and spend the night and the following day transiting to that area.