To engage units using artillery strike you have to be in the artillery units' radius. The radius is approximately 32 km.
| Please note:
In the start of the campaign the artillery units are often occupied by another job. But after 15 minutes (use timespeed) units become available.
A good to terrain for a try out is the Taiwan - War of Independence map. On the west coast (playing blue team) there are a lot of artillery units south of those many tanks in the plain.
After you made a request, please be patient, it can take a minute or so.