CREATE TABLE table_name_71 (date VARCHAR, where_sunk VARCHAR, ship_type VARCHAR)

What is the date that a hell ship sunk in the East China Sea?
SELECT date FROM table_name_71 WHERE where_sunk = "east china sea" AND ship_type = "hell ship"
SELECT "date" FROM "table_name_71" WHERE "east china sea" = "where_sunk" AND "hell ship" = "ship_type"