Never use arty bde for amphib invasions. Some players use marines + arty, but they detach the arty bde and land them separately to reunite them. Personally I prefer to 3 marine divisions of 5 bde for amphib invasions: that packs the most punch while being very powerful [but this is manpower + IC expensive].
Same idea for arty: all bde effects are averaged, so adding arty to mountain bde will give you a little more firepower but will slow down the division in lots of terrain.
see
http://www.paradoxian.org/hoi3wiki/Terrain
for more details about terrain effects.
Same idea for arty: all bde effects are averaged, so adding arty to mountain bde will give you a little more firepower but will slow down the division in lots of terrain.
see
http://www.paradoxian.org/hoi3wiki/Terrain
for more details about terrain effects.