Bataille Empire

Two infantry units are facing off in a fire fight at volley range. The non-active player's unit has a battery by its side. We played the following sequence.
1) The active player nominates the two infantry as the primary shooters.
2) The infantry of the non-active player must return fire as this is volley range.
3) The artillery has a target at cannister range and we ruled that it must fire in support.

The controversial part was no 3. The reactive player would have preferred to wait to activate the battery in his own turn. We felt the requirement to return fire at cannister range did not permit this. Were we correct?

Hi all.

As the artillery units is not the target of the ennemi units it can wait to fire later in the turn.

Supports are never compulsory.

Thanks, one more item that needs more clarity in the rules.