Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_5680 ( "Gauge" text, "Railway" text, "Class" text, "Works no." text, "Year" text, "Builder" text )

### Question ###
Which works number has a class of 15th and year of 1940?

### Accurate SQL ###

SELECT "Works no." FROM table_5680 WHERE "Class" = '15th' AND "Year" = '1940'