user: Question: Which tonnage has a Date of 26 September 1940, and a Ship Name of Ashantian?
Columns: ['Date', 'Ship Name', 'Flag', 'Tonnage ( GRT )', 'Fate', 'Deaths']
Types: ['text', 'text', 'text', 'real', 'text', 'real']
Sample row: ['26 September 1940', 'Ashantian', 'Great Britain', 4917.0, 'Damaged', 4.0]
SQL:

assistant: SELECT "Tonnage ( GRT )" FROM "Table" WHERE "Date" = '26 September 1940' AND "Ship Name" = 'Ashantian';