Through the switch from steam to gas turbines, one part of the propulsion system, the reduction gears, stayed. The gas turbine helped reduce a ship's weight by eliminating the heavy steam turbine casings and boilers. To circumvent this last hitch, the Navy installed controllable pitch propellers, which can direct their thrust backward. Controllable pitch propellers also help to maintain steady turbine speed even as ship speed changes during maneuvers. But to make the controllable pitch system work requires a complex network of hydraulics running through the propeller shaft.
Electric drive severs the connection between prime mover and propeller.
Electrical generators can be located anywhere on the ship, their power transmitted through cables to the propulsion motors. The same generator can provide power for propulsion, combat systems, auxiliary equipment, and ship's services. According to Whitcomb, a typical naval combatant might need 50 to 100 megawatts for propulsion, and another 5 to 15 MW for hotel loads and weaponry. Gas turbines tied mechanically to the ship's propulsion are unavailable to supply the electrical power needed by other systems. Thus, additional smaller-capacity gas turbine or diesel generators must be carried on board and dedicated to producing electrical power.