In a true diesel–electric transmission arrangement, by contrast, the propeller or propellers are always driven directly or through reduction gears by one or more electric motors, while one or more diesel generators provide electric energy for charging the batteries and driving the motors. While this solution comes with disadvantages as well as advantages in comparison with the direct mechanical connection between the diesel engine and the propeller that was initially the most common arrangement, the advantages were eventually found to be more important. One of several significant advantages is that it mechanically isolates the noisy engine compartment from the outer pressure hull and reduces the acoustic signature of the submarine when surfaced. Some nuclear submarines also use a similar turbo-electric propulsion system, with propulsion turbo generators driven by reactor plant steam.