Datasheet for this transistor?
It's probably a manufacturer's internal part number. You'd have to find the service manual for the equipment it came from and see whether it provides a cross-reference to a generic part number.

Otherwise, the best you can do is reverse-engineer the circuit it came from and figure out what capabilities it had to have to work there. It's actual capabilities are (presumably) greater than that.

A transistor curve tracer would also give you some clues, along with knowing the power capacity of the TO-3 package that it's in.