To provide a propulsion system for a large ocean-going marine vessel having a hydraulic supply system improved in flexibility and efficiency.

The propulsion system for a large ocean-going marine vessel includes: a cross head type large two-cycle diesel engine connected to a propeller via a drive shaft; one or more power generation facilities each including a prime mover and a generator, for generating electric power irrespective of an operation condition of the large two-cycle diesel engine; a high pressure hydraulic pump station or a pump driven by one or more electric motors; and a hydraulic piston motor connectable to the drive shaft or the propeller shaft for providing power for returning when the large two-cycle diesel engine becomes faulty.