user: Question: Which Tonnage (GRT) is the highest one that has a Date of 16 June 1940?
Columns: ['Date', 'U-boat', 'Name', 'Nationality', 'Tonnage (GRT)', 'Fate']
Types: ['text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['21 November 1939', 'U-21', 'HMSBelfast', 'UK', 11500.0, 'Damaged (mine)']
SQL:

assistant: SELECT MAX("Tonnage (GRT)") FROM "Table" WHERE "Date" = '16 June 1940';