Recess Rumble: Fighting Tank Destroyers
Tank Destroyers have access to some of the best guns in the game. As such, it's generally inadvisable to drive right up to one across an empty field and try to destroy it from the front. The odds are you'll be a smoking wreck before you get there.
How do I defeat tank destroyers, you ask?
The answer is simple. Stay alive and minimize your exposure to them. Tank destroyers can shoot you from range, so depending on your battlefield role, you want to spot the TDs, stay alive to relay their location to your team, and flank them when the opportunity presents itself rather than attempting to match them shot-for-shot from the front. Most of the time you try to do so, you will lose.
As a light tank: Tank destroyers have powerful guns, but their view range is not as good as yours. As you do your job spotting along the fringes of an engagement, you will want to keep an eye on the locations and paths of the enemy force to relay back to your team. This is the ideal time to look for an isolated tank destroyer that can't see you. Then, you can spot the TDs for your teammates, and even fire at them or knock off their track before you get around to the side and deal some damage when they are distracted!
As a medium tank: Medium tanks have the visibility to out-spot tank destroyers, the mobility to get around to their vulnerable flanks and the firepower to do some serious damage from the sides and rear. Your speed and turret traverse allow you to move your tank and gun around faster than the enemy TD can traverse their chassis, which moves the gun. While your first choice should be to out-spot the enemy tank destroyers and engage them from a distance with your team, you can run circles around most TDs up close.
As a tank destroyer: Your main defense is the spotting range and proximity of allied tanks. Rely on your team to spot targets for you, and focus on removing enemy vehicles from the game one tank at a time. Rather than spreading your shots out and leaving four enemies at half-health, it is better to knock out two tanks completely, depriving enemy TDs of spotters and protectors. If the battle comes down to a 1v1 fight with another TD, you will often want to stay stationary on favorable ground, possibly near your cap circle, and wait to get the first shot in. Pay close attention to your sub-class and the strengths and weaknesses of the enemy TD. If you are more mobile or have a turret, use your speed advantage and flexibility to anticipate and engage the enemy TD in a way they cannot match.
As a heavy tank: As a heavy tank you can use terrain and thicker armor to get up close and personal as you blast away! This is where the game changes, because now you can take hits and sacrifice some HP to deal damage and knock TDs out of the game. You have two main strategies for engaging tank destroyers:
1) Angling your armor: As you peek around or over terrain to take shots at enemy TDs and pull their attention away from fragile teammates, make sure you only expose your turret and/or frontal armor.
2) Taking a hit or two to get in close: Bait the enemy TD into taking a shot at you before knocking out their track and maneuvering alongside them. Once you're in close, fire shots into their weaker side armor while they cannot shoot back! You may have to take one or two shots from the enemy along the way, but as a heavy tank, you can usually eat those hits and survive. Remember, the only hit point that really matters is the last one on your tank.