Surely everyone has seen one of these tanks if you've played blitz. These tanks are beasts. Simply put, if you see one, you are in for some pain. I'm going to teach you how to deal with these tanks, and how to use them.
When you start off as the T18, you'll have an average tier II gun. I suggest upgrading that first, before anything. Once you have the howitzer, your problems in this tank are over.
How to use it
The T18, with the howitzer, and hopefully the good engine and tracks, is a beast. In level 2 battles, you will dominate. Unlike the AT-1, which has a similar high damage gun, you have tremendous armor. Most level 2s will find it hard to hit your one weak spot, on the upper front plate, especially when you are dealing 200 damage consistently against their thin armor. You have good turret traverse, so it will be harder to flank you. You have superb speed, making you a well armored, tank ramming, HP destroying fury. The only tank you should worry about is another T18, which can deep you in one shot just as fast as you can derp it.Most of the times, you can just aim and shoot on any other TD and one shot them, in your tier. Any level 1 gets one spotted. Most level 2s and 3s will take a huge amount of damage, often half or more of their total hitpoints. However, I must mention one tank which stands out when facing the T18 though. The Pz.II.
Facing the T18
I have crushed this tank numerous times as well, sometimes with the Pz.II, the T18, and even once in a while, the T1 Cunningham. So this tank is not invincible. This is how to face the T18 with the derp, respective to tier.
Tier I
What's wrong with you? That tank will one shot you the second it sees you. Run foo! If you really want to face him, you'll have to get him in the back, and even then it's not guaranteed.
Tier II
Among the tanks I've used, the Pz.II is the most effective against it, except for the At-1 and T18. More often than not, you will find a glaring weak spot on the T18 frontal armor, the upper plate. Here you can one shot the T18 using the T18 or AT-1 with their own derp guns. If you are the Pzjg II, run for your life, cause this guy can and will one shot you without aiming. If using a Pz.II, you will find that your semi automatic gun can pen the T18 frontally at its weak point. Furthermore, your armor is thicker than most, so you can actually hold off against one. The T18 can pen you if you stay still, so keep moving. The T18 deals two types of damage. One is from 60-80, which happens if it hits any slightly armored or "red" part of your armor. The second is when it deals around 200 damage. This is scary. Very scary.
Tier III
At this tier, you won't be as scared of this tank. It can deal respectable damage, but everyone can damage it back, and your pen will be far better. All in all, you still have to watch out for this tank, but don't run from it.