CREATE TABLE table_34839 ("Locomotive" TEXT, "Pre-conversion" TEXT, "Entered service  ( T ) " TEXT, "Re-entered service  ( P ) " TEXT, "Owner" TEXT)

Who owns the locomotive that entered service on 30 October 1956?
SELECT "Owner" FROM table_34839 WHERE "Entered service (T)" = '30 october 1956'
SELECT "Owner" FROM "table_34839" WHERE "Entered service (T)" = '30 october 1956'