At the beginning of each research branch (except the U.K.) is a Tier I light tank of the corresponding nation. Light tanks are small in size, have small caliber guns, and low armor thickness. However, they offer a high rate of fire and good dynamic characteristics: a high maximum speed and great maneuverability.
In your first battles, it's mostly light tanks that you'll come across. However, having reached the mid-level battles, you will be seeing them less infrequently or never at all, since currently the maximum light tank Tier is IV (A-20). And while in low-level battles you can fight vehicles of other classes on an equal footing, one should be extremely cautious when going into battle on the A-20 tank against, say, Tier V vehicles. In such situations, your main task lies in helping out your high-level allies however you can: spotting enemy forces allows the team to choose the direction of attack or prepare for defense; or enveloping the enemies to briefly distract them or to attempt to inflict damage, shooting up their sides and rear. If the battle is far away from the base, you can step in to capture and distract the enemy, retreating at first sight of danger.
In medium and high-level battles, light tanks are replaced by medium tanks. Stats of medium tanks, such as speed and maneuverability, armor and firepower, vary greatly. As a rule, medium tanks' gun caliber and armor thickness is inferior to that of heavy tanks. The key difference between medium and heavy tanks is their mobility. They are more mobile, meaning that if necessary, they can quickly regroup or immediately fall back to base if the enemy attempts to capture it.
In general, medium tanks are all about versatility: they can wear any hat on the battlefield, depending on the situation and the balance of power in combat.
Play in a tag team with another medium or heavy tank, as this greatly increases the chances of defeating each individual enemy tank that you might come across.
Compared to medium tanks, heavy ones typically have thicker armor and a powerful gun. These tanks usually spearhead the attack, drawing the bulk of the enemy fire, while high HP count and better armor allow withstanding a significant number of hits.
It is the fearlessness of heavy tanks that often provokes rivals to ill-considered actions. This will help you breach enemy defenses, single-handedly defend a certain direction, or survive base capture. But even these armored Supermen have their kryptonite. Unfortunately, many heavy tanks are clumsy, meaning they may be vulnerable in close quarters against a more mobile rival. It’s also worth remembering that heavy tanks (like all others, to be fair) are best protected at the front, with weaker rear and side armor.
Anti-tank self-propelled artillery systems (tank destroyers) have, as a rule, the biggest guns. But since the barrel is so huge, most of them have no turret, so they have to turn the entire vehicle to face the enemy when firing. That's why tank destroyers are better placed at significant distances from the enemy forces, enabling them to fire at the largest area of the battlefield without turning their hull. This will also keep you away from maneuverable light and medium tanks that can easily "jump" you, causing damage to the poorly armored sides and rear.
Try, as early into the battle as possible, taking a position that offers a good viewing range, as well as the ability to fire at the largest area of the map. Alternatively, choose one that offers cover for most of the hull. If possible, take cover behind thick bushes to conceal your location. Then, when your team reaches numerical superiority, leave the shelter and support the offensive until victory is yours!