use of onagers and other heavy artillery

[NihilisticCow]

Onagers with fire are pretty wildly inaccurate (certainly compared to them without fire). If your enemy marches toward you, you will (unless you're very lucky) simply not do enough damage to their forces to justify the cost of the onagers. Onagers do come into their own however with a camped enemy, even if they have onagers. As you can move your onagers up to attack them, so they will then target yours with theirs. But the difference will be, when you miss their onagers you will be hitting their troops.

If you outnumber the enemy onagers, then they will be forced to attack you (or take large casualties), but if you are outnumbered you should attack (where you will outnumber them with your normal forces - the more enemy onagers, the greater your advantage).

One thing though, I would never set onagers to fire at will - you will probably take far too many friendly casualties when you are closer together, besides it is always best to target the densest parts of the enemy formation.