Lately I've been thinking about WoT in the terms you would use for PvP in any proper MMO. This has mostly been an effort to try and easily categorize the different tank classes and come up with quick explanation about their purpose. Some of us may already get this, but for the sake education here it is:
Heavies: They should considered the "tanks" of WoT, and like a tank in other MMOs they are the primary meat-shield of any team. They deal enough damage to hold their own, but not anywhere the same amount as the ranged DPS classes. Heavies should focus on either preventing access to a part of a map, or spearheading an attack. In either case, it isn't so much that the heavy should let themselves get hit, but they should atleast draw enough of the enemy's attention that fast tanks can flank, and support classes (TDs or SPGs) have a chance to actually support the heavy. Certain heavies are better at one role more than the other, and the map as well as the circumstances of battle will determine exactly what strategy a heavy should use.
Mediums: They are the melee DPS class, fast and powerful enough to catch an enemy off-guard, but also not tough enough to take on a bunch of enemies alone. Mediums don't typically have enough armor or HP to defend as well as a heavy can, but in an emergency it is a viable tactic. Mediums are best used as close/mid range support for other tanks. Whether they are supporting a heavy or a wolf-pack depends on the circumstances, but the same applies, "haul ass and bypass". Instead of attacking an enemy directly, mediums should either allow a more heavily armored tank to aggro the enemy tanks, and attack them from the sides. Heavies would do well to call out the target of priority so that both the heavy and mediums can focus their firepower effectively. When in a wolf-pack you have safety in numbers, and each member of the pack should take a turn shooting at the enemy. It should be decided beforehand which medium is going to lead the pack as far as calling out targets, and the lead vehicle should alwasy be prepared to be the first one to recieve fire.
TDs/SPGs: Ranged DPS/Caster analogies here. Certain TDs are tough enough to fight close in, but most do not. Arty, hide and do your thing. Other than that, the game mechanics dont allow for a more detailed comparison. Basically do not go it alone as a TD, even the toughest TDs can be outmaneuvered and ganked. TDs are better served by thinking of them as snipers in an FPS, when picking a location to cover, do not try to take on more than you can handle alone. More than likely you will be spotted once you fire, so position yourself so the only person who can shoot back is the poor bastard you just hit.
Probably the most important thing we can try to do as a team is know who we are tanking with, who is the lead tank for each group, and all target the same vehicle.
