How modern a warship could operate in the 1860s?

How new could a warship be and still function if sent back to the 1860s?

There is no agreed cutoff: proposals range from older steam-and-sail ships to coal-fired dreadnoughts and ships burning low-grade oil, depending on what operating requires.

The answers depend on whether operating means crossing oceans or remaining an effective fighting ship. A coal-fired dreadnought is one proposal, while another view favours an older ship with sails to reduce dependence on purchased coal. Ships using low-grade fuel oil or mazut are also proposed, although that suggestion depends on suitable fuel handling and supply. The preference for an Iron Duke-class battleship rests on its coal-fired machinery and overwhelming armament against contemporary opponents. There is no agreement on one latest acceptable date or one design. Whether new ammunition could be made becomes a separate point of dispute.