[ahartmetz]

Much harder to hit though, except with modern precision bombs if you happen to know where they are.

That said, I also doubt that bomb resistance was the main reason for underground power lines. The sentiment in Germany at the time was, and mostly still is today: "No more wars!"

[PaulDavisThe1st]

I'm not sure it is much harder than hitting aerial wires, is it?

Presumably, you aim for the substations anyway, which I think are generally above ground no matter where the wires are ...