Shortly after White arrived on station, ''Plunger'' was seen by a Japanese destroyer which came on using powerful echo-ranging sonar—or "pinging." Hearing the pinging was a jolt. The submarine force had not known for certain, until now, that the Japanese had such gear. The Japanese not only had it, they knew how to use it. The destroyer found ''Plunger'' and unleashed twenty-four close depth charges. It was a vicious, determined attack, the first for both the hunter and the hunted in Empire waters. It jarred the boat and crew severely. White was thankful that he had put back into Pearl Harbor to repair the weakness in the hull. Had he not, ''Plunger'' might not have survived.

While on this patrol, White nearly sank a ship by accident that would have caused an international uproar. Through diplomatic channels, President Roosevelt had arranged an exchange of political prisoners trapped in the United States and Japan by the outbreak of war, including U.S. Ambassador to Japan Joseph C. Grew. They were put aboard the neutral vessels ''Asama Maru'' and S.S. ''Conte Verde'' for transfer from Japan to the United States. They were to sail with lights and other markings on a prearranged route, as would the vessels returning the Japanese.
On 5 June, () English had sent instructions to his submarines, describing these ships, the routes, and the markings. Later, on 25 June, when the vessels actually got under way, English sent further messages, designed to assure immunity from submarine attack. Dave White failed to receive these messages. In the early morning hours of 30 June, he picked up ''Conte Verde'' and began an approach, somewhat astonished to find a ship all lighted up.
Back at Pearl Harbor, George "Turkey Neck" Crawford was on duty that night in submarine headquarters. "The Communications Officer," Crawford remembered, "came in to see me and wanted to send the immunity message again. I checked through the files and discovered that we had sent it four nights in a row. I questioned the need to send it again. However, the Communications Officer thought it might be a good idea, so, somewhat reluctantly, I put it on the air."
On ''Plunger'', White had ''Conte Verde'' fixed in his periscope hairs and the crew at battle stations when his communications officer, having picked up and just decoded this fifth immunity message, rushed up into the conning tower. White broke off the attack at the last minute, settling for a photograph taken through the periscope from a range of 800 yards.