welcome to the forum Kanesoban [:)]
The artillery at this stage of the war is very powerful, and fast to respond to calls for fire.
It is used primarily for softening up an enemy position prior to an attack, and for breaking up enemy attacks, or concentrations, like during the reorg phase of an attack.
Your units will enter a state of retreat, in proportion to the number of casualties they have sustained. It represents their reluctance to "step in to the breach" because of what they have just seen happen to their comrades.
It also gives them time to tend to the wounded, and steel themselves for the next attempt at carrying out your orders.
When in formation either under a Bn HQ or above, the units try to stay in that formation.
If one of the units in the formation is unable to advance, because of fatigue, or retreat recovery, the whole formation will wait for that unit to fall back into formation before it will continue the advance.
The AI currently is very bad at dropping the incapacitated unit, and continuing with the advance.
When you see that the advance has halted because one of your units has sustained very heavy casualties, and has gone into retreat recovery, pause the game and assess the objective.
If you think that the objective can be taken with your remaining units that are still in good health, then you have two options.
You can either drop the retreat recovering unit by giving it a defend in situ order, then re order the attack with the HQ. If you do this the HQ will first have to catch up to the new FUP you order.
Or as I normally do, give the HQ a defend in Situ order, then give the remaining line units individual orders to attack.
This is the best option in my opinion for a lightly defended position, because if one of the units goes into retreat recovery the others will continue on to the objective.
If the objective is heavily defended however, or a long way away, you could run the risk of them being picked of individually as they arrive piecemeal at the objective.
Take a look at this image it also has a few tips to help with artillery mitigation:
tm.asp?m=3360428
If you have any more questions, just ask, I will be happy to help if I can.
Which side are you playing in We fight o die here?