A basic knowledge that every soldier must learn is knowing the difference between cover and concealment. 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 an important one 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 a concealment. This can range from bushes and tall grass (especially at high graphic 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, thus leading to victory. Concealment can also hide downed pilots to escape enemy visual detection. Even non-objects, such as shadows, can hide an appropriately camouflaged soldier and hence making it a 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.
Any object that can protect someone from incoming fire is called cover. This can range from cars and trucks to tanks or buildings. Generally, a cover is also a concealment because a soldier can hide from sight as well. Cover, like concealment, is relative. Not every solid object is a cover for everything. 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 cover for 9 mm rounds, such as wooden fences, that do not protect against 7.62 mm rounds. A successful soldier should know what protects from what.
Cover versus Concealment Edit
A soldier hiding behind a bush, tall grasses or a brick wall is harder to spot than another soldier standing in the open. If the enemy found him and start shooting at him, the bush and grasses will offer no protection against the incoming fire. While the wall 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 brick wall is both a concealment and, to a limited extent, a cover while bushes and tall grass are simply concealment.
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.