Alright, I must admit I have had a love affair with mortars for a very long time, but then GW decided to bring out a younger and sexier woman and I have wandered to her. The Wyvern is hands down amazing, its 5 pts more than a mortar squad and has all the buffs you could need rolled into one package. That being said, mortars themselves are not gone, but how you can use them is different than before since the wyvern fills the role so well. You should still look at taking mortars, but mortar squads are not the top choice anymore.
Mortars have a couple of advantages over wyverns that still make them a usable weapon. As a mortar squad, its hard to take them unless you are building an all infantry fluffy list. As a heavy weapon for squads though they are still a good choice to take. They are dirt cheap when purchased as part of a squad, with three costing 15pts, and the other bonus they have over wyverns is that they can accept orders, importantly pinning to gain that oh so useful rule back. Yes other weapons can benefit from this as well, but the power of indirect fire and how wounds are allocated in ruins or multilevel terrain is not to be underestimated.
Mortars & Orders
Mortars on their own aren't that amazing, S4 AP6 isn't bad but isn't amazing either. Where mortars start to get better is through orders. The first order that is up on the list is suppressive fire that grants pinning. Barrage lost pinning in 7th, a huge blow to their effectiveness in neutralizing targets. With this order you can get this back. This is very useful against middling to low leadership units, especially support based ones like pathfinders that tend to hole up in hard to reach places. Use this order on these targets to pin them in place and keep them from acting effectively. This still is effective against standard marines with Ld8, though not highly reliable, you throw enough pinning out and squads will start to go to ground. Since only one model has to take a wound (unsaved), you can neutralize units like pathfinders and scouts without dedicating significant fire towards them. This also is good to use when you are planning to charge a unit, using pinning to force that unit to ground and give up its overwatch, as long as they fail the check. Tied into this is to not use it on units with very high Ld or fearless or other rule that ignores pinning checks.
The ignores cover order can be very good when used against the right units. A good example light units that have stealth and more often than not have a better cover save than armor. Using this order in conjunction with mortars against one of these units can be very good. Now you can mitigate the units cover, maximizing the chances of those wounds actually killing these models. Mortars a great because these units are easy to wound and they are also relatively low leadership as well, forcing a morale check and hopefully breaking them. The hard part of this order is that you will have a lot of units that you will want to put this on but only so many times you can use it. Whether you use it or not is going to depend on the importance of the targets that you need to neutralize. If you really need ot kill a jinking wave serpent, then use ignores cover on something else, but if you really need to get rid of light infantry unit dug into good cover, notably ruins as they still provide cover whether LoS is blocked or not. The point being to use the mortars with this order to maximize their effectiveness and take advantage of barrage. Note this works well against non MEQ bikes as well who rely on their better jink save vs their armor to get them across the board. The trouble you may find is that they may opt to not jink because you used the order, and in some cases it is better to have the units reduced shooting effectiveness.
Another order that is good when used effectively is the shoot and run order (forward for the emperor). This is best on units with mortars in them like PCS and blob squads, allowing you to shoot with your units and then run with them, giving you movement without sacrificing firepower. This is situational but good if you have an assault unit advancing towards you and need to fall back, or want to shoot a unit off of an objective and then move onto it. This is good again for a infantry units with mortars or other heavy weapons that want to shoot and move.
Mortars & Support
The other thing to remember with mortars is that they are there to support your army. Where they are very good at is when they are used in conjunction with lasgun fire. Now I touched on this in my last article but it is worth noting again how using lasgun fire to weaken units to that critical point where mortars can tip them over the edge and increase your chances of causing a pinning check and ending the effectiveness of that unit.
Mortars also work well in supporting your infantry when it is charging, since they cannot fire lasguns and charge, this means that unit will only be using a few shots from assault weapons and won't have much fire to increase its chances of succeeding in the charge. Now this is where mortars come in. You fire them at the unit you want to charge and make up for their lack of fire, and weaken it to increase your chances of winning the charge. Where this is effective is because of barrage, wounds are allocated on the hole, not direction of fire. So you can reduce the squads size but not increase your charge range by have models in the middle and back suffer the wounds. This also means they will have to take a pinning check if you use the order(you should), that can be the difference between swinging first or last, and with guardsmen low initiative, this is a big difference. Also try and use the benefits of barrage to target characters and flamers, the squad losing its auto hit over watch weapon or only combat model being a huge effect on the ensuing assault phase, this is far more important for them to lose their sergeant with power weapon and flamer, then to kill four regular guys, the effect those models having on combat being far higher than the standard troopers.
They also work great in the opposite roll, stopping enemy charges. Again what this all boils down to is taking advantage of pinning with the order. One wound causes a pinning check, and if that unit fails, it has turned from a big scary unit into a target waiting to die. Now be aware what you are shooting at and don't go shooting at fearless units and wonder why they keep on coming. Now against units like tyranids, the key to taking advantage of this is using other weapons in your army to remove that "fearless" i.e. synapse. Using lasguns to whittle the orks down to a point where the mortars can cause enough wounds to give you the best chance on their mob rule roll, and to use other weapons to remove the synapse threat and then use the mortars on the now un-fearless squad. And if all else fails, use mortars to try and pick off combat characters and special weapons with barrage to make that assaulting unit less scary.
Using Mortars
As already mentioned, the Wyvern competes a lot with the old mortar squad, as its only 5 pts more but does so much. Mortars are now best used in squads as their heavy weapon. A PCS is a great choice as well as in combined squads. It provides cheap anti infantry fire power that can target units out of sight. You can also use them in mech armies, where the mortar can fire out of the hatch of the chimera, giving you additional indirect fire as well as protecting them and the squad they carry.
Now a mortar squad can still be used, don't get me wrong, and it will still do well. Its just that a wyvern will do the same job better. If you are taking mortar squads, then be sure to protect them and take advantage of objective secured and orders to maximise their damage. They are easily squished on their own if they don't have protection and with no natural pinning, you'll have to dedicate orders to it and not something else to get its effectiveness back. Its better not to and just let them fire and force morale checks and use orders on other units.
Overall mortars are a great and cheap support weapon that can help infantry out a lot if used with the right orders and support. The hits to barrage do hurt them somewhat but with orders they remain just as effective as before. I'll still be using them, just slightly differently than before.
Well I hope you find this useful and if you have a used your mortars in other ways I am all ears.
GG