CREATE TABLE table_61231 ("Ship" TEXT, "Hull Number" TEXT, "Laid down" TEXT, "Launched" TEXT, "Commissioned" TEXT)

What is Launched, when Laid Down is '31 October 1981'?
SELECT "Launched" FROM table_61231 WHERE "Laid down" = '31 october 1981'
SELECT "Launched" FROM "table_61231" WHERE "Laid down" = '31 october 1981'