Mortars could be described as the common soldiers artillery gun. Mortars are basically a small versions of artillery guns that shells over a high arc on a target location.

In Darkest Hour both the allied and the axis team have access to mortars on most maps. While both mortars work the same way there are a few things that are not the same between the axis and the allied mortar. The axis mortar can shoot on much shorter distances than the allied mortar but has a smaller overall distance. However the high explosive shells of the axis mortar have a bigger area damage effect as the allied mortar. The allied mortar on the other hand can shoot over longer distances (but not as short as the axis mortar) andthe high explosive shells have a smaller damage area. I doubt it was intended like this but the allied mortar can damage every vehicle in Darkest Hour exept for the higgins boat, so it is in fact possible to damage or to destroy a Kingtiger with the allied mortar. Both the axis and the allied mortar can fire smoke shells and they work and behave the exact same way.

To use mortars effectively you need two players. One will take the role of the operator and the other one will take the role of the observer. The observer has the job to find targets, mark them and also help the operator to range in his fire. The operator is the player who is actually deploying the mortar, selecting the correct elevation and traverse settings on the mortar and firing away the shells.

Let us have a look on observer first.

Observers usually have the same weapon loadout as a normal rifleman with the exeption that he also has binoculars. The binoculars are used to find and mark targets for the operator. You select the binoculars with your weapon selection keys. When you have the binoculars selected you can press the key with that you would usually bring up the iron sights of weapons to look through the binoculars. When you are looking through the binoculars and you have found a target for the mortar simply look at it and press your fire key. You should see a message in the upper left corner that you have marked something for the operator. When you now open your map you will also see a red crosshair icon which is marking the spot on the map that you have just marked. In general only mortar operators and observer are able to see the mark on the map. If you want to cancel a mark simply select the binoculars and press your melee key.

Now let us take a look at the operator.

As a operator you will spawn with the mortar in both of your hands. While you hold the mortar you are not able to sprint, jump or going prone. To deploy the mortar press your deployment key. This is the same key you use to attach your bayonet or to use a bipod. Once the mortar is deployed you can enter or leave it at enemy time by pressing the use key. When you are not on the mortar you can move like any other player on the map, which means you can sprint, jump etc.
When you are actually on the mortar you see in the down left corner some numbers and letters and a scale. You can pretty much ignore the scale, what really counts are the numbers below it. The first thing under the scale is showing you if you use high explosive shells or smoke shells. When you deploy a mortar you always have high explosive shells selected first. Below that you find the settings for traverse and elevation. To make it simple the traverse settings change how much your fire goes out left and right while the elevation settings change how long or short your shells are going. The smaller the elevation is the longer your shells are going while the higher the elevation settings is the shorter your shells are actually going.

As already said unless you are a pretty experienced mortar player you will need a mark by a observer to really know where your shells are landing (even if you are a experienced player you will do much better with a observer and it is way more fun). So when the observer is marking a target you should deploy the mortar in the direction to the target. After that you fire a shell with a elevation setting that could be close to the mark. If you dont know the map well my advice is you select a smoke shell for that to avoid teamkills and use the standard elevation setting of 75.0. When your shells are landing close enough to the target (around 200m) you will see a small explosion icon on the map. This icon is marking the the impact of the last shell that you have fired. With that information you should be able to figure out if you are shooting to short, too long, too much to the right or too much to the left. If you do not see that explosion icon you are not hitting close enough and in that case you better ask your observer or other players if they know where your shell was landing. If the marks of the observer constantly disappear, he is dying a lot. When the observer dies, his mark will also disappear. So as a observer play defensive and support the team buy giving accurate markers as long as the mortar is not on target.

I hope this small guide explained how you actually use mortars in DH. If you have any feedback or suggestions feel free to post them.