On 31 March, that group was dissolved, and "Threadfin" received orders to join and near Bungo Suido, the primary entrance to the Seto Inland Sea which separates Honshū from Kyūshū and Shikoku. The new attack group's primary assignment was to guard against an undetected sortie of the remainder of Japan's fleet during the Allied assault on Okinawa. On the evening of 6 April, "Threadfin" made radar contact with what later proved to be an enemy task force built around Japan's super battleship, . Passing up a tempting opportunity in order to carry out her prime directive, "Threadfin" flashed the warning to Fifth Fleet headquarters afloat off Okinawa.