Enlisted

This is probably the most difficult achievement in the game.
Nevertheless, as they say, the devil is not terrible, as it is painted
I just want to say that it is almost impossible to make 30 kills per match on a flamethrower, so you should not be attracted to getting a squad of flamethrowers at the 5th level of progress in the Battle of Normandy.
So it is better to throw all the forces to get a squad of mortar men (they open at level 14 in each of the battles).
This process is not fast, but by this time you should understand all the principles and mechanics of the game, spawn points, etc.
After the opening of the mortar squad, we need several matches to reach the 3rd level of the squad, thereby upgrading the ability to take an engineer to our squad.
Then you can start completing the achievement.
Ideally, we need the map "Village of Vysokovo" and the Invasion mode, a game for protection.
We appear on the map, our engineer builds boxes of ammunition. Even one will be enough, because our bots for some reason like to break them
Then we sit down near the box so that we can replenish the shells by simply turning the camera, and start shooting at the trenches.
The range of the mortar is set +/- the same as the distance to the capture point.
If the ammunition in the crate is out, the engineer can build two more. And if in the rest, too (which is unlikely) then we return the engineer under our control, break down and build the boxes again.
In this cunning way, we can stay in our rear all the time and have an almost infinite number of shells

UPDATED SOLUTION - MAY 2024

I believe the solution wrote for this is outdated due to updates to the game recently. This is an updated solution. Probably wrote a little too much, but the game throws a lot of information at you and has a lot of menus, so I tried to explain it all if your new to the game.

-HOW TO UNLOCK MORTARS- (Ignore if you already have the mortar unlocked.)

You will first need to unlock mortars on one of the four teams, you can see if you have them unlocked by tabbing over to research tab on the home screen with . If you press or , it will switch the 4 teams that are available, each team has different items to unlock with research points. You earn points just by playing the game, the more points you get in-game, the more research points you will earn.

I personally chose Japan and used the Type 89 Mortar, but I believe all the mortars work the same on the different teams. I wouldn't pick Germany though, as you will have to research 2 items before you can start researching the mortar for that team, instead of just 1 item for the other teams. You start researching an item by clicking on it and pressing , then MAKE SURE you have the team your doing the research for selected at the top before going into a game and check that the "Join any team" option is unchecked in the right bottom corner, that way it won't put you on a random team and you will be earning points for the correct team.

Once researched, you will unlock a squad with a Mortar person in it, you will need to assign the mortar person to an existing squad or put the new squad in your lineup at the home screen on the left. I'd explain this more, but honestly I found it a bit confusing, you will eventually get it.

-UNLOCKING THE ACHIEVEMENT-

Once you have mortars researched and you have a person with a mortar on one of your squads, it's time to unlock the achievement. Press on the home screen and you should have the option for "CUSTOM MATCHES", select that. Press again to create a game, these are the settings you want.

Main Settings:
Game Mode: Squads
Difficulty: Standard
Max Players: 20
Max AI-soldiers: 20
Campaigns: Invasion of Normandy
Server: North America (It shouldn't matter though.)

Armies:
Pick whichever team you unlocked the mortar on.

Missions: (It's a little over half way down the list.)
Invasion
River crossing North (Allies)

Press to create the game. Make sure your on the red team, then start the game. Select your squad with the mortar person and spawn in. You will want to run towards the first objective and stop when your around 90 away, then pull out your mortar and aim it towards the objective, you can set the distance on the mortar with , make sure it's set around 90, doesn't have to be exact. Start firing, the mortar bullets don't land in the same spot and will land randomly in the area that it's aimed, so moving it a little to the right/left won't really help. Fire all the bullets, even the smoke ones, as I believe I got kills with them somehow.

I got 32 kills on my first attempt, but redoing it, I was only getting around 20-28, which is fine. If you didn't get at least 20, quit the game, reload it and try again, you won't have to change the settings again. Once you get at least 20 and are out of ammo, press both and and press the kill soldier option, you will have to do this for each solider in the squad. Then you can pick a new squad and repeat this process until you can select the mortar squad again.

Once you have the mortar team again, head to whatever the next objective is and do the same thing we did at the first objective. DON'T shoot at it if your team is already capturing it, as there aren't going to be many enemies at it. If you didn't hit 30 kills yet, you can repeat the process we just did to get the mortar team again and try at the next objective, or the next one after that, eventually you will get it though, it may just take a few attempts. The achievement won't pop during the game, so you can finish out the game, or quit the game through the menu and the achievement will pop, it may take a minute or two, as mine did.

(An alternative method to unlock this achievement is to research a flamethrower, which is pretty far down the research tree. Then go into a private lobby with a dummy/friend and kill them 30 times with it. Probably will spend more time doing that method, though it's an option. You can't do this with the mortar because the mortar shots are random and don't land in one place.)

If you have any questions or see a mistake, let me know. This map I chose may not be the best one, but it worked for me as the first objective is out in the open, so the AI doesn't have anything to hide under when the mortars hit.

UPDATED SOLUTION - MAY 2024

I believe the solution wrote for this is outdated due to updates to the game recently. This is an updated solution. Probably wrote a little too much, but the game throws a lot of information at you and has a lot of menus, so I tried to explain it all if your new to the game.

-HOW TO UNLOCK MORTARS- (Ignore if you already have the mortar unlocked.)

You will first need to unlock mortars on one of the four teams, you can see if you have them unlocked by tabbing over to research tab on the home screen with . If you press or , it will switch the 4 teams that are available, each team has different items to unlock with research points. You earn points just by playing the game, the more points you get in-game, the more research points you will earn.

I personally chose Japan and used the Type 89 Mortar, but I believe all the mortars work the same on the different teams. I wouldn't pick Germany though, as you will have to research 2 items before you can start researching the mortar for that team, instead of just 1 item for the other teams. You start researching an item by clicking on it and pressing , then MAKE SURE you have the team your doing the research for selected at the top before going into a game and check that the "Join any team" option is unchecked in the right bottom corner, that way it won't put you on a random team and you will be earning points for the correct team.

Once researched, you will unlock a squad with a Mortar person in it, you will need to assign the mortar person to an existing squad or put the new squad in your lineup at the home screen on the left. I'd explain this more, but honestly I found it a bit confusing, you will eventually get it.

-UNLOCKING THE ACHIEVEMENT-

Once you have mortars researched and you have a person with a mortar on one of your squads, it's time to unlock the achievement. Press on the home screen and you should have the option for "CUSTOM MATCHES", select that. Press again to create a game, these are the settings you want.

Main Settings:
Game Mode: Squads
Difficulty: Standard
Max Players: 20
Max AI-soldiers: 20
Campaigns: Invasion of Normandy
Server: North America (It shouldn't matter though.)

Armies:
Pick whichever team you unlocked the mortar on.

Missions: (It's a little over half way down the list.)
Invasion
River crossing North (Allies)

Press to create the game. Make sure your on the red team, then start the game. Select your squad with the mortar person and spawn in. You will want to run towards the first objective and stop when your around 90 away, then pull out your mortar and aim it towards the objective, you can set the distance on the mortar with , make sure it's set around 90, doesn't have to be exact. Start firing, the mortar bullets don't land in the same spot and will land randomly in the area that it's aimed, so moving it a little to the right/left won't really help. Fire all the bullets, even the smoke ones, as I believe I got kills with them somehow.

I got 32 kills on my first attempt, but redoing it, I was only getting around 20-28, which is fine. If you didn't get at least 20, quit the game, reload it and try again, you won't have to change the settings again. Once you get at least 20 and are out of ammo, press both and and press the kill soldier option, you will have to do this for each solider in the squad. Then you can pick a new squad and repeat this process until you can select the mortar squad again.

Once you have the mortar team again, head to whatever the next objective is and do the same thing we did at the first objective. DON'T shoot at it if your team is already capturing it, as there aren't going to be many enemies at it. If you didn't hit 30 kills yet, you can repeat the process we just did to get the mortar team again and try at the next objective, or the next one after that, eventually you will get it though, it may just take a few attempts. The achievement won't pop during the game, so you can finish out the game, or quit the game through the menu and the achievement will pop, it may take a minute or two, as mine did.

(An alternative method to unlock this achievement is to research a flamethrower, which is pretty far down the research tree. Then go into a private lobby with a dummy/friend and kill them 30 times with it. Probably will spend more time doing that method, though it's an option. You can't do this with the mortar because the mortar shots are random and don't land in one place.)

If you have any questions or see a mistake, let me know. This map I chose may not be the best one, but it worked for me as the first objective is out in the open, so the AI doesn't have anything to hide under when the mortars hit.