With the Japanese destroyer bearing down on them, they had only moments and the first torpedo missed. The second one had to get a hit or they would be depth charged out of existence. Morton did not fire his second torpedo until the bow of the destroyer was only 750 yards away. Since the torpedo needed to run 700 yards before it armed, this was as close as you could cut it. Immediately on firing the second torpedo, Wahoo went deep but as she did so the destroyer fired a full pattern of depth charges which exploded very close to the Wahoo and gave her a beating.
[Sources: Execute Against Japan: The US Decision to Conduct Unrestricted Submarine Warfare by Lt. Joel Ira Holwitt, USN and Wahoo: The Patrols of America’s Most Famous World War II Submarine by Richard H. O’Kane (three stars).]