Call of Duty: WWII

Before you start each mission you need to manually select Veteran difficulty, as it will not continue on Veteran.

There are 11 missions in total.

A few quick tips I've learned:
1. Take your time. Your platoon will kill enemies too, and enemies are not infinite spawning.
2. Smoke grenades. Smoke grenades are amazing in this game as they blind the enemy. If you are ever under heavy fire and trapped in a position, throw a smoke grenade and advance to a new position.
3. Manage your health. Health does not auto-regenerate this year, you need health packs. After clearing out an area check for any health packs and always try and keep your health above half.
4. Use your teammates. This year you are able to use your teammates to give you ammo/health/mortar attacks/grenade refills/enemy scouting. Use all of these to your advantage as often as you can.
5. Use cover wisely. If you crouch near a wall or a car and hold the to aim you will pop out allowing you to shoot, and as soon as you let go of the you will be back in cover.
6. Don't get flanked. There are a lot of close quarters encounters in this campaign. Make sure you slowly work your way through, don't rush ahead of the enemies as you will get pinned down and shot from behind.

I've also made a video for EACH mission of the campaign on veteran, so if you are stuck in a particular section or want to prepare yourself I would recommend using them:

Figured I'd make my own guide since a couple of people have confirmed my method works. YOU DO NOT HAVE TO PLAY THROUGH THE ENTIRE GAME ON VETERAN. There is a glitch in this game that is very similar to the glitch on Modern Warfare Remastered, which means you can play the vast majority of the game on Recruit and only play specific sections on Veteran. There is inevitably a lot of text in this guide, however don't let that put you off as the glitch is extremely simple to do. If you want to get straight into how to do the glitch, skip the next couple of paragraphs and read the numbered instructions further down. If you're already familiar with the MW Remastered Veteran glitch, there's a TL;DR at the bottom of the guide. If you have no idea what glitch I'm talking about, continue reading on.

Doing the glitch and playing through the missions on Recruit is miles easier than trying to play through the game on Veteran. Doing the glitch also means you don't have to replay missions for miscellaneous achievements, as some of them are next to impossible to do if you try doing them on a "legit" Veteran playthrough of the game. I did the glitch myself in December 2019, and the person I know to have most recently performed this glitch successfully got this achievement in October 2020. The game hasn't had updates for a while and there's unlikely to ever be any updates/patches for the game (the last DLC was released in 2018). Even if there are any patches, it's extremely unlikely they're going to patch anything relating to the campaign.

The glitch is essentially the same as the glitch for MW Remastered, with an extra step. In MW Remastered you only need to complete the final checkpoint of each mission on Veteran, whereas for WWII you need to complete both the first and final checkpoint of each mission on Veteran. I'm not sure why this is, it's just what I found when I played the game. If you've already tried doing the MWR glitch after reading some of the comments on the other guide(s) and not gotten the achievement, the chances are that you've not played through the first checkpoints of each mission. In that case, load up each campaign mission on VETERAN and play until you see checkpoint reached. You can then save and quit and repeat this for all the missions, which should only take you 15 or so minutes.

Onto the glitch:

1) Load up whatever mission on VETERAN, or if this is your first playthrough select a new game on Veteran. Play through the mission until you see checkpoint reached. Normally this is right at the start of the mission when you first gain control of your character, however you might have to move a little or engage in some gunfights. Do not do step 2 until you see checkpoint reached appear on your screen.
2) After you've seen checkpoint reached, pause the game and lower difficulty. Each time you lower the difficulty it will lower the difficulty once, so you need to go into the menu and lower the difficulty 3 times to end up on Recruit (Veteran - Hardened - Regular - Recruit)
3) Continue playing through the mission on Recruit, doing any miscellaneous achievements and grabbing mementos/doing heroic actions on the way. If you miss anything you can die and reset checkpoints as much as you like, you'll still be playing on Recruit difficulty.
4) When you get to the last checkpoint of the mission, save and quit. Note, it doesn't have to be exactly the last checkpoint, it's just the more you do on Recruit the less you have to do on Veteran which makes it easier. If you're not sure where exactly the last checkpoint is on a mission, there's normally a big gunfight or escape sequence at the end of the mission. The important thing here is that you don't accidentally complete the mission on Recruit, as then you'll have to do the entire mission again to do the last checkpoint on Veteran.
5) After saving and quitting the game, do the glitch the same way you would do it for other COD games. Load up the same campaign mission and select Veteran difficulty. It will ask if you want to restart the mission and lose all current progress, select yes. Whilst the mission is loading up, dashboard and force quit the game. Load the game back up, go onto the campaign and hit to resume the campaign from the last checkpoint. You'll now be at the same point in the mission on Veteran.
6) Complete the mission on Veteran.

Once you've done this for every mission, you will have almost every campaign achievement with 1 playthrough of the game. The only thing you might have left to do is using the abilities (which is an easy grind). This glitch is super easy to do, and it makes the completion of this game possible for anyone willing to put in the time. If you're still reading, thanks for checking out my guide! If you leave a negative, please state why so I can improve the solution.

TL;DR - Do the same glitch you do for MWR, then spend 10-15 minutes starting up each mission again on Veteran and playing through until you first see Checkpoint Reached. You can save and quit after hitting the first checkpoint on Veteran, there's no need to fully complete the mission.

EDIT: I've had a few people message me saying this doesn't work on the Series X/S. This does still work on the Xbox One, so if you're having problems either try this on the One or use the other solution to go through the levels legit.