user: ### NOW ANSWER:
Question: When did Chatham complete the HMSMedusa?
Columns: ['Name', 'Builder', 'Laid down', 'Launched', 'Completed']
Types: ['text', 'text', 'text', 'text', 'real']
Sample row: ['HMSMarathon', 'Fairfields, Govan', '10 August 1887', '23 August 1888', 1889.0]
SQL:

assistant: SELECT "Completed" FROM "Table" WHERE "Builder" = 'Chatham' AND "Name" = 'HMSMedusa';