So... I was thinking of the interesting suggestion for a Forward base and well... THIS came to mind. I assume you people remember the huge railway guns built by the germans... If not, then here's a special image just for you!
Impressive, eh? Well then, perhaps you could ability to build something similar. Probably some huge artillery cannon that could be placed in empty nests connected to cities which would then begin the process of shelling the city and destroying its infrastructure. Sounds like a good idea?