nick0515
A while back I wanted to represent the modern use of cruise missiles on ships so I increased their bombard range to that similar as cruise missiles in the game. Added them to subs, too. This was in addition to their normal attack and their ability to carry other items like nukes, aircraft and land units. The same missile representation can be done with land units, either straight artillery units or perhaps with other AI flags set also. I have not tried the latter, but the former, others have gotten the AI to use land artillery with blitz, a higher move factor and a higher bombard range.
Rockets tend to carry larger warheads than shells so their bang on arrival is much larger. As others pointed out, these are area saturation weapons, but not very accurate against individual targets. Their effect is usually greater, when used in quantity, that regular artillery, since a lot more can arrive at the target at one time. Their downside is long reload time. Shot off all at once, or in a few salvos, rockets are quickly gone and it then takes a while to load up the launchers again. Regular artillery can keep up a more steady bombardment. Another difference is artillery rockets use HE blast, rather than velocity more than regular gun artillery, so a well protected fortification, or ship, can resist rocket fire better than it can gunfire. Ballistic missiles and high speed cruise missiles can mimic this aspect of gunfire, with their higher velocities, but the usual artillery saturation rockets are smaller and arrive at the target with lower velocities.
In game mods, I tried representing this difference by giving rocket artillery a higher bombard factor than regular artillery, but a lower rate of fire number. I also adjusted the hit points of units according to the unit's resistance to this difference in attack types. More hit points to represent more armor and better resistance to HE. This gives the rockets a larger chance of inflicting damage, but with less chance of each individual shot killing a unit with higher HPs set (If the unit's HPs are greater than the attack ROF, an attack can not kill it. So if I want a unit to be immune from destruction from the attack of another in one on one combat, I give the unit more HP than the ROF of the attack of the other.). With lethal artillery set and the use of multiple units firing at the same target, this is very powerful, and can represent saturation attacks, and destroy units that would be resistant to the attack of a single unit.
With gun artillery given a lower bombard factor, but higher ROF, the individual artillery attack has more "staying power" to cause deeper damage to the unit (shave off more HPs), but less likelihood of hitting in each micro round of the combat resolution, so that while a hit is harder to obtain, the damage can be worse and the unit can possibly die from a single encounter.
I also used this idea to differentiate between attack bombers and strategic bombers. To do this, I also adjusted the amount of damage needed to destroy buildings and lower pop in cities to work with this. By giving strategic bombers a high bombard, but lower ROF, they are less likely to destroy units (and unable without lethal set), but more likely to knock out buildings and lower pop in citiy attacks (since buildings and pop do not have HPs). Tactical bombers are given a lower bombard, but higher ROF. They can destroy units easier, but their lower bombard in relation to buildings and pop, makes them less likely to hurt cities.
Hope this makes sense. It's easier to set in the editor than describe on a forum.
Edit: I've tested this stuff using the Combat Calculator and by putting units against one another in test scenarios, but I have never tried it in a full game.