Blitzkrieg- Help I'm confused.

[gorham09]

I'm new to Blitzkrieg and I am just starting out with the Allied campaign. I am confused about assigning my core units in the campaign missions. I have three tanks and three artillery pieces, yet the only units available in the mission are the tanks (there are other non-core units- trucks, infantry, etc.) but the artillery does not appear. I was wondering how do I assign which of my six units make it into a given mission?

Any Blitzkrieg veterans out there that can help a confused newbie