If you want AI to bombard:
Drop artillery power by half.
Give artillery a 75%->84% withdrawl chance. (75% for primitive, 80% for gunpowder, 84% for modern).
Give artillery a +100% hillls and city defence bonus. (just as strong as before)
Give artillery a +100% collateral damage bonus. (just as strong as before)
If the unit had odd strength, round down, and grow the +100% bonus's. (ie, catepult goes from 5 to 2, and gains +150% city/hills defence & collateral. The trechpult goes from 4 to 2, and gains +300% city defence, +100% city attack, +100% hills defence, +100% collateral: 8 city defence (same as before), 4 hills defence (same as before), 4 city attack (1/2 before), 4 collateral strength (same as before), 2 general attack (1/2 before)).
Replace promotions with:
Supply Train:
I: +10% heal rate in friendly/neutral lands
II: +10% heal rate everywhere
III: +10% heal rate everywhere, +10% heal to units in stack
// artillery take lots of damage when attacking. This lets the artillery "reload" faster
City Assault:
I: +40% city attack, +10% bombard defences
II: +40% city attack, +10% collateral
III: +40% city attack, +5% bombard defences, +5% collateral
// at +120%, a new catepult is a 9.6
Fire Volume:
I: +40% collateral
II: +20% strength, +50% collateral
III: +10% bombard defences, +60% collateral
Range:
I: +5% withdrawl chance, 1 extra first strike
II: +5% withdrawl chance, 1 extra first strike
III: +5% withdrawl chance, 1 extra first strike
Precision:
I: +5% bombard defences, +30% strength, 1 extra first strike
II: +5% bombard defences, +50% city/hill defences
III: +10% bombard defences, +40% collateral, +40% strength
...
Note the bonuses above are large. This is because I halved the unit's stats -- doubling of the modifiers, adding +100% at the units specialty, and halving the stats, makes a unit that is half as effective. (ie, 2 +100% +40% is the same as 4+20%).
To bombard, you simply attack with a siege unit. Your base attack will be half what it used to be. (with city attack III you get +120%, but your strength was already halved. So you are are instead at your old strength +10%.)
You have a base 75% to 84% withdrawl chance, so your unit will probably not be destroyed. Improved range III boosts this to 90% to 99% withdrawl chance.
The city and hill defence bonus' make placing artillery in a city still useful, and in the field they can be used to defend difficult terrain. However, in the open, they are extremely vunerable. Cannon can still route primitive warriors in an open field battle, but it isn't very efficient.
The goal is that AIs know how to use this kind of unit. Your cannons "lead the charge", but this really reflects bombardment. Sometimes an enemy manages to destroy one of your cannons during the battle, which is relfected by a withdrawl failure. Increased range makes it harder for the enemy to take out your catepults (represented by increased withdrawl chance).
Drop artillery power by half.
Give artillery a 75%->84% withdrawl chance. (75% for primitive, 80% for gunpowder, 84% for modern).
Give artillery a +100% hillls and city defence bonus. (just as strong as before)
Give artillery a +100% collateral damage bonus. (just as strong as before)
If the unit had odd strength, round down, and grow the +100% bonus's. (ie, catepult goes from 5 to 2, and gains +150% city/hills defence & collateral. The trechpult goes from 4 to 2, and gains +300% city defence, +100% city attack, +100% hills defence, +100% collateral: 8 city defence (same as before), 4 hills defence (same as before), 4 city attack (1/2 before), 4 collateral strength (same as before), 2 general attack (1/2 before)).
Replace promotions with:
Supply Train:
I: +10% heal rate in friendly/neutral lands
II: +10% heal rate everywhere
III: +10% heal rate everywhere, +10% heal to units in stack
// artillery take lots of damage when attacking. This lets the artillery "reload" faster
City Assault:
I: +40% city attack, +10% bombard defences
II: +40% city attack, +10% collateral
III: +40% city attack, +5% bombard defences, +5% collateral
// at +120%, a new catepult is a 9.6
Fire Volume:
I: +40% collateral
II: +20% strength, +50% collateral
III: +10% bombard defences, +60% collateral
Range:
I: +5% withdrawl chance, 1 extra first strike
II: +5% withdrawl chance, 1 extra first strike
III: +5% withdrawl chance, 1 extra first strike
Precision:
I: +5% bombard defences, +30% strength, 1 extra first strike
II: +5% bombard defences, +50% city/hill defences
III: +10% bombard defences, +40% collateral, +40% strength
...
Note the bonuses above are large. This is because I halved the unit's stats -- doubling of the modifiers, adding +100% at the units specialty, and halving the stats, makes a unit that is half as effective. (ie, 2 +100% +40% is the same as 4+20%).
To bombard, you simply attack with a siege unit. Your base attack will be half what it used to be. (with city attack III you get +120%, but your strength was already halved. So you are are instead at your old strength +10%.)
You have a base 75% to 84% withdrawl chance, so your unit will probably not be destroyed. Improved range III boosts this to 90% to 99% withdrawl chance.
The city and hill defence bonus' make placing artillery in a city still useful, and in the field they can be used to defend difficult terrain. However, in the open, they are extremely vunerable. Cannon can still route primitive warriors in an open field battle, but it isn't very efficient.
The goal is that AIs know how to use this kind of unit. Your cannons "lead the charge", but this really reflects bombardment. Sometimes an enemy manages to destroy one of your cannons during the battle, which is relfected by a withdrawl failure. Increased range makes it harder for the enemy to take out your catepults (represented by increased withdrawl chance).