diesel electric option in S3d

[fw66]

Hi,

I've been looking at the sim files of subs using s3d and have noticed that under 'unit_submarine' there is a 'Is_DieselElectric' option under 'Ballast'.

The description says: 'Specifies whether the sub is diesel-electric or normal'

So, if 'true' is checked, does this mean diesel electric in the sense of having diesel engines turning the propeller shaft on the surface and electric motors when submerged?

If yes, then what is considered to be 'normal'?

Or, does it mean diesel-electric drive system (like a British U-class), where even on the surface, the electric motors turn the propellers, and the diesels act simply as a power source?

Also, since the game already has the properties of the sub's propulsion, what effect would this feature actually have?

Thanks for any info!