Overall, remember that an army is about the projection of firepower. Each type of unit protects another unit that has longer range and/or firepower. Front line units do NOT have to win the war or even do most of the fighting. They are there to hold ground. This is especially important on Expert Difficulty, where the enemy has more health than you do, so they will always be able to outfight you if you both have equal circumstances. The difference is tactics.
Scouting cannot be underestimated. Knowing both where the enemy is, and is NOT, is key. The latter is very hard in Company of Heroes because the missions are frequently scripted with "cheats" where the enemy will literally just magically pop out of nowhere, even in areas you had previously cleared, and even when nowhere close to a map border (and cannot thus be called "reinforcements from off map"). You see an excessive amount of this in Normandy Mission 2.
Some map elements, such as buildings and thick rows of bushes can let both you and the enemy see each other. However, only enemy mortars will try to attack you. The others do not generally move. Sometimes you can be close enough to throw a grenade or satchel charge over the barrier. This generally works for bushes, but not for buildings -- You can still throw an explosive, but it will detonate inside the building.
Try to scout with Sniper pairs: One ahead always in camouflage, the other farther behind, taking the shots. This way, you can both scout and advance. If you have only one Sniper, you can still clear enemy clumps:
- Back off until you see only one unit.
- Shoot that unit.
- Move the sniper immediately away so that you won't be spotted by the other enemy units wandering in the direction of the dead unit.
This does not work when the enemy is in a building because units inside buildings have a longer line of sight, longer than the sight range of your sniper on the ground.
Do not move your sniper into a building, because that just lets the enemy know a hostile is inside the building.
The main danger in this approach is actually nothing you can control: Enemies may spawn in response. Again, you see this a lot in Normandy Mission 2, where approaching a Strategic Point, capturing a Strategic Point, or killing all units at a Strategic Point will almost always cause a squad to spawn and move to its location.
Anti-Tank guns have a longer sight range than infantry, and therefore can sight for your heavy machine guns, allowing them to set up safely and start firing. When you have nothing else, you can use an AT gun to spot. There is no "Hold Fire" option, so to prevent them from firing, you will need to deploy them so that there are no enemies in their arc of fire.
Killing two members of a 3-unit squad typically causes the third unit to automatically die.
Typically these are deployed on the map without their gun ready to fire. That way, the enemy can set up their gun quickly and facing the correct direction. In order to flank a HMG unit, you therefore need to have at least two squads, and even if you don't lose any units, you will lose health on that team, putting you closer tol losing members.
Use snipers or mortars against them. If you use a sniper and cannot flank them, always shoot the gunner first. This will force another member of the 3-man squad to take control of the gun, meaning only the third member can shoot at you with their regular firearm.
Whenever you attack, you are briefly visible. When mortars attack, they are also briefly visible, even if not normally so because you do not have a unit in range to see them. When a unit is hit, they are also briefly visible in this way.
- For the enemy, this means that if you are in range, it will attack as soon as you expose yourself. Move your squad immediately. You can do this to do mortar-versus-mortar.attacks, as the enemy mortar will typically NOT move except to change firing direction or if it is moving closer.
- For you, this means that as soon as you hear the distinctive launching sound, you can pause the game and immediately scan the map for the enemy mortar.
Use snipers or mortars to deal with enemy mortars. If you use a squad of soldiers, rush them. The main danger here is if the area near the mortar crew is not clear and has troops or maybe a HMG team.