user: Question: What's the departed date that the HMS Leith of the Royal Navy?
Columns: ['Name', 'Class', 'Navy', 'Date joined', 'Date departed']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['HMS Bluebell', 'Flower class corvette', 'Royal Navy', '18 October', '21 October']
SQL:

assistant: SELECT "Date departed" FROM "Table" WHERE "Navy" = 'Royal Navy' AND "Name" = 'HMS Leith';