The answer depends on what you are trying to do:
If you just want the mortar guys to fire in a general direction, but you don't really care if they hit a certain target, then you need to use the "fire" command. That will make them fire in whatever direction they are looking at... so first you need to make them look in the general direction using the dowatch command.
If you want the mortars to actually HIT their target, then things get more complicated. If your mortars are always going to be in the same place, and the same goes for your target, then you COULD just do the above, but keep adjusting where they look until it hits where you want. But this will only work when everything is in the same place, and you don't move anything in the editor after you set it up.
If the mortars or targets might be moved or in a different place, then you are in need of some very complicated scripting. Luckily the brains over at the Chain of Command have made an addon that will do just that. It is called "Unified Artillery", and you can find it here on OFPEC, or on thechainofcommand.net, or on any other addon site.
There is also an old script here that actually makes tanks fire like artillery... I'd really suggest you use UA, but it MIGHT work, so you may want to check it out:
http://ofpec.com/editors/resource_view.php?id=213
Topic: need mortar squad to fire a position when trigger activated (Read 723 times)