A basic principle that every soldier must learn is knowing the difference between cover and concealment, and how to use them. No infantry, or even ground vehicles, will survive long should it disregard cover in a battle. The ArmA series is sufficiently detailed to make this aspect crucial should a player want to succeed. This article is written primarily with infantry in mind, although with some adjustments, this can also be applied to ground vehicles.
Any object that can hide someone from sight is considered concealment. This can range from bushes and tall grass (especially at high graphics settings) to buildings. Transparent objects like glass windows are therefore not concealment. Concealment allows a soldier to approach the enemy position without being detected and surprise the enemy, making it easier to defeat them. Concealment can also hide downed pilots to escape enemy visual detection. Even non-objects, such as shadows, can hide an appropriately camouflaged soldier, thus making it a form of concealment. Concealment, especially with the use of night vision and thermal sights, is relative. A soldier behind a bush may be hard to detect visually, but will show up easily on thermal scopes on enemy helicopters. Good intel will help soldiers to determine what may hide them from the enemy.
In tactical movement during a firefight, one of the most useful forms of concealment is smoke. Smoke can be deployed via infantry through smoke grenades, via artillery through smoke shells, and via vehicles through smoke screens. Once it has been deployed, it can allow infantry and vehicles to advance upon, retreat from, and most importantly to flank around an enemy position, even in an open field or around an exposed hilltop.
Any object that can protect someone from incoming fire is called cover. This can range from cars and trucks to tanks or buildings. Generally, cover is also concealment because a soldier can hide from sight as well. Cover, like concealment, is relative. Not every solid object is effective cover against every type of weapon. In the ArmA series, like in the real world, different rounds have different powers and as such have different penetration. A 9 mm round does not travel as far or hit as hard as a 7.62 mm rifle round. This means that there are objects which provide cover against 9 mm rounds, such as wooden fences, but which do not protect against larger calibers like 7.62 mm rounds. A successful soldier should know what barriers provide effective cover against the enemy's weapons.
Cover versus Concealment Edit
A soldier hiding behind a bush, tall grass or a short wooden fence is harder to spot than another soldier standing in the open. If the soldier is spotted and begins taking fire, the bush and grass will offer no protection against the incoming fire. While the fence may be enough to stop a 9 mm round from a Makarov pistol, it is certainly no protection against the 120 mm cannon of the M1 Abrams or even heavy machine guns like the DShKM or M2. This means that a wall or fence is both a form of concealment and, to a limited extent, a form of cover while bushes and tall grass are simply concealment. Meanwhile, sturdier walls, like H-barrier walls, are effective concealment and provide cover against practically everything, including 120 mm tank cannons.
The mission editor can be very useful to test penetration of different weapons and learning about concealment. This can be done by setting up targets behind various cover and putting units in different terrains to see what can hide the units under different conditions.