user: Question: Which nation had a Battlecruiser with an estimate of 513?
Columns: ['Estimate', 'Name', 'Nat.', 'Ship type', 'Where sunk', 'Date']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['9,000', 'Wilhelm Gustloff', 'Germany', 'Cruise ship', 'Baltic Sea', 'Jan 30, 1945']
SQL:

assistant: SELECT "Nat." FROM "Table" WHERE "Ship type" = 'Battlecruiser' AND "Estimate" = '513';