user: Question: What is the nationality of the ship when the principle victims are Civilians?
Columns: ['Estimate', 'Name', 'Nat.', 'Ship Type', 'Principal victims', 'Date']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1255.0, 'HMS Queen Mary', 'UK', 'Battlecruiser', 'Crew', 'May 31, 1916']
SQL:

assistant: SELECT "Nat." FROM "Table" WHERE "Principal victims" = 'Civilians';