Range of fire for on map artillery division

[Gris]

Well I have fired my heavy rocket division several times, with no effect at all on fortifications.  In the north I built 3x heavy breakthrough divisions and stacked them and attacked, out of 6 attacks only once did I reduce the fortifications by .02%.

In v1.04.10 - April 18, 2011 -Artillery (especially Heavy Artillery) can cause small fort reductions during combat. 

I don't recall actual numbers in the manual. I would say engineers are effective and artillery helps. Artillery and Forts is very common when searching through the manuals, but I will see if I can find some more info.