Direct steam, turbo-electric, and diesel-electric drives

Which propulsion system is best: direct steam, steam turbo-electric, or diesel-electric?

The best choice depends on period and requirement: direct drive favors simplicity, turbo-electric drive offers flexibility, and diesel-electric drive favors range.

The preferred machinery changes with the period and the ship's requirements. Direct steam drive offers mechanical simplicity, while turbo-electric drive provides greater flexibility after battle damage or machinery casualties. Electric transmission also allows shorter propeller shafts and connects the main machinery through cables, reducing the long shaft routes along which water can travel. Diesel-electric drive favors range, with a possible tradeoff in maximum speed. Better electrical power transfer, batteries and combinations of power sources improve the efficiency available from electric drive. Frequent high-speed running before the Second World War also left destroyers needing substantial refits.