changing of army types

[unmerged(2591)]

Sometimes,when I attack and besiege provinces,it happens that my infantry and cavalary just transform into artillery.I thought of that they might have died,but it seems like the size of the army is as big as it was.Does anybody know if they're just killed or are they "transformed"?

 

[unmerged(2073)]

I think you mean that a cannon appears and starts bombarding the province. If so, this is just the symbol to tell you that you are besieging the province and doesn't change the make up of the troops or give you any cannon. Just click on the army and you'll get the siege scree which will tell you the make up of the siege force (and the besieged)