HAT shooting

[saamohod]

A short question. How to shoot the damn Heavy Anti Tank? Last time I played this game a couple of years ago I didn't have problems with it. But now I only managed to pick up a HAT kit, aimed at a target, presses left mouse button, ... and nothing happened. I saw an unintelligible writing in the bottom right of my screen each time I pressed the fire button. And right after that I was killed.
What did I do wrong?

[Mineral]

There is a SEEK delay.

[saamohod]

There is a SEEK delay.

So what do I do? Do I keep the fire button pressed? How long does it last?

[Murphy]

Hold the trigger for 3 seconds, the delay is tricky but it evens the playing field.

[DesmoLocke]

Hold left click and don't let go. You will be rewarded.