CREATE TABLE table_68769 ("Estimate" TEXT, "Name" TEXT, "Nat." TEXT, "Ship type" TEXT, "Where sunk" TEXT, "Date" TEXT)

What is the date that a hell ship sunk in the East China Sea?
SELECT "Date" FROM table_68769 WHERE "Where sunk" = 'east china sea' AND "Ship type" = 'hell ship'
SELECT "Date" FROM "table_68769" WHERE "Ship type" = 'hell ship' AND "Where sunk" = 'east china sea'