紀伊水道
Refit brought the replacement of "Seadragon"'s three-inch deck gun with a four-inch gun, and, on 1 April, she cleared Pearl Harbor for the Japanese home islands for her tenth war patrol, with James H. Ashley, Jr. (Class of '34), at the helm. On 5 April, she crossed the International Date Line. On 15 April, she entered Japanese waters. On 16 April, she moved past O Shima, and, that night, commenced patrolling off the Bungo Strait and Kii Channel entrances to the Inland Sea. On the morning of 23 April, she sighted four freighters, escorted by three patrol boats, moving toward Shiono Misaki. She closed the convoy; fired on the third ship, the heaviest laden; then went deep and rigged for depth charging. The patrol boats moved toward "Seadragon" as "Daiju Maru" sank and, during the next two hours, delivered a 40 depth charge attack. Later that day, the submarine conducted an unsuccessful attack on a naval auxiliary; and, on 26 April, she moved out into the Tokyo-Manila shipping lanes where she damaged a freighter on 27 April.