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: