It was based on purchase icon. Some parts taken from German Nebelwerfer for more details.
SAM site and patriot will be in mod. Both are missile batteries but will act differently. SAM site will fire volley of missiles, each with low damage, patriot will fire two missiles at time with high damage.
I do like the idea of a nebelwerfer being the inspiration, it fits the Allies
some base at the bottom would make it look better ingame. But thats just me.