Many navies are engaged in building a new generation of electrically powered ships. These have many advantages such as numerous, dispersed drive units.
Today’s invention is a new form of drive unit for large ships.
Such vessels, eg aircraft carriers, would be fitted with a special underwater docking mechanism to which a nuclear submarine (or two) could attach themselves.
This would happen only if the carrier needed to get somewhere at twice its normal speed, since it renders the submarine more vulnerable than normal.
Since these subs have enormous potential power outputs, they could add their propulsive force to that of a carrier, without a correspondingly large increase in combined drag.