The American aircraft carriers Lexington and Saratoga were built in the 1920s, converted from the unfinished hulls of battlecruisers made redundant by the Washington Naval Treaty of 1922. One of their innovative aspects was a relatively new kind of engine, the turbine-electric. Rather than driving the propellers through a series of gears, the steam boilers in the Lexington and Saratoga drove electrical generators. The electricity then powered electric drives in the rear of the ship which turned the propellers. This new set-up was supposed to have advantages of economy, efficiency, the ability to reverse the propellers quickly, and better low speed operations. Popular Science proudly labeled the new engines as a “major revolution in shipbuilding.”  The Society of Naval Architects and Marine Engineers agreed:
The fact that the last nineteen capital ships of the U. S. Navy are or will be equipped with the electric drive is sufficient testimony in behalf of what the builders and users of war vessels think of its merits. The prime requisite of reliability in any type of machinery designed to propel war vessels was recognized in the electrical machinery at the time of the first installation. Also the calculations showed that the unit fuel consumption over a wide range of operating speeds should be better than anything yet proposed. Service operation of two 30,000-horse-power electrically propelled battleships has indisputably proven that the reliability is all that was claimed, and that the fuel economy, as compared with other ships of the same type using direct-connected turbines with geared cruising turbines, is vastly superior.
Two other factors in which the electric drive shows a marked improvement over other drives have been emphasized since the first battleship was built, namely, the superior protection from torpedo attack afforded the machinery by virtue of the arrangement of the electric plant and the superior maneuvering qualities of the electric drive. The large horse-power requirements of the present war vessels (60,000 horse-power and 180,000 horse-power) preclude the use of reciprocating-engine drive, and this leaves electric drive with a decided maneuvering advantage over any other form of turbine drive. 
This turned out to be optimistic. The advantages noted were offset–as the Navy was to discover in WWII–by problems. The turbine-electric propulsion systems were more vulnerable to shock damage than ordinary, geared engines, flooding of the engine compartment required time-consuming and expensive repairs, and the power/weight ratio of the turbine-electrics was much worse than of conventional engines. 
But that was in the future. As built, the Lexington was essentially a large power plant with a side helping of warship. Each of its four electrical generators could put out 35,200 kilowatts, in total “enough to supply the electricity demands of a city the size of Philadelphia.” 
Strangely, as it turned out, the Lexington served as a power plant long before she saw a day of combat.
(Part II coming on Monday)