CREATE TABLE table_55399 ("Ship's name" CLOB, "Date entered service" CLOB, "Date withdrawn" CLOB, "Tonnage" FLOAT, "Type of Ship" CLOB)

what is the sum of tonnage when the type of ship is twin screw ro-ro motorship and the date entered service is 11 february 1983?
SELECT SUM("Tonnage") FROM table_55399 WHERE "Type of Ship" = 'twin screw ro-ro motorship' AND "Date entered service" = '11 february 1983'
SELECT SUM("Tonnage") FROM "table_55399" WHERE "Date entered service" = '11 february 1983' AND "Type of Ship" = 'twin screw ro-ro motorship'