For clarification (from an off-line question).
Command units (COs & HQs) that have an AA designation in their Notes, can only shoot using Opportunity fire (or as part of defense against enemy air-strikes).
They cannot fire at enemy ground units and if they fire using Opportunity fire they will have a +1 penalty added to their CV rolls for orders that they issue in the next game turn (as is standard with all units that Opportunity fire).
Many thanks
Mark