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_name_87 ( tonnage INTEGER, date VARCHAR, name_of_ship VARCHAR )

### Question ###
What was the average tonnage for Beatus, raided on 18 October 1940?

### Accurate SQL ###

SELECT AVG(tonnage) FROM table_name_87 WHERE date = "18 october 1940" AND name_of_ship = "beatus"