Final answer:
The exact year when Hospital Stewards were authorized by Congress to be appointed by the Secretary of War and mustered as NCOs is not provided in the reference material and further research is required to provide an accurate answer.
Step-by-step explanation:
The year when Congress authorized the Secretary of War to appoint Hospital Stewards as Non-Commissioned Officers (NCOs) and muster them onto hospital rolls has its roots in the civil war period. However, as the provided reference materials do not contain a specific year related to the direct authorization for Hospital Stewards to be appointed by the Secretary of War, an exact year cannot be provided without further research into historical records.