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 ship ( ship_id number, name text, type text, nationality text, tonnage number )
TABLE: CREATE TABLE mission ( mission_id number, ship_id number, code text, launched_year number, location text, speed_knots number, fate text )

### Question ###
Show the types of ships that have both ships with tonnage larger than 6000 and ships with tonnage smaller than 4000.

### Accurate SQL ###

SELECT type FROM ship WHERE tonnage > 6000 INTERSECT SELECT type FROM ship WHERE tonnage < 4000