by bdegroot
An Op Fire is an action.A24.1— Actions may be announced by either player at any time via a Fate card played from the hand so long as that Action’s listed condition or prerequisite is met. Multiple Actions may be conducted in response to the same game situation. All effects of consecutively- played Actions are cumulative.
So lacking a leader you could use multiple Fire action cards on multiple adjacent units and form a fire group for the Op Fire shot against the moving unit(s).