How to destroy the tank? [spoilers inside]

[Csimbi]

Hi,
I am at mission 3.
I grab the grenade launcher, then what? How do I destroy it?
I keep firing at the tank with the launcher (from a safe distance), but nothing happens - ever. It does not seem to penetrate the armour.
On the other hand, zie Germans keep coming and if I get a few bullets from the tank, I am dead.
I found a destroyed tank earlier on the level - that's burning on the top - so I thought I need to aim at the engine. Tried, but again, nothing happens.
A few hints would be nice.
Thanks.