Starcraft Education 2 - Hitting from out of range

Warriors,

You must still remember my defeat in a previous game when I was rushed by the evil Druggy - bahh, he put his sunken right outside of my base and shoot it OUT OF RANGE!! Somehow he managed to kill the tank from afar and we all wonder, what secret technology has he learnt to make this happen??

Now my fellow warriors, after spending hours and hours into my research I have finally found out about this most advanced and secretive move of Druggy, and have it unveiled before your eyes, so you can all judge how evil he has been!!

SC Education 2 - How does your unit achieve infinite range?

Introduction

All SC units, when attacking must "prepare" for the attack action. For marines they have to "hold up the guns", for hydras they have to "open" their mouth, etc.

So SC units' attack are carried out in the following sequence:

1. Select a target in range
2. Prepare for attack
3. Carry out the attack action

But, if such sequence is interrupted in between the 2nd and 3rd phases, the following will occur:

1 Select a target in range
2. Prepare for attack
3. Found a target with higher priority
4. Carry out the attack action

Note that when the new target is selected, phase 1 is no more carried out and the unit can theoretically attack ANYTHING it targets (with higher priority) without the range constraint. Thus, such unit would've got INFINITE range of attack - EVIL!

So that explains why the poor tank was taken out even if it is not in the sunken's range of attack:

1. The Sunken was going to attack the factory (or something else I can't remember) - phase 1. It has prepared for the attack action - phase 2.
2. The tank, sieged outside of the sunken's range, hit the sunken (the tank's range is longer than the sunken).
3. The sunken found the tank to be a higher priority target - phase 3, hit the tank immediately.

The following replay shows you the whole sequence (see sunken take out out-of-range cannon at 12 o'clock position).

Replay

And you will ask:

Question:

Hei what happen when we use tanks to siege a zerg base full of sunkens - just like what we did always? Wouldln't the sunkens take out the tanks?

Answer:

Nope. The sunken must be attacking something first (in range), so that it can finish its 1st and 2nd phase of attack, then must be hit by the tank at this particular time (right after it finishes preparing, and before the attack action actually happens), so it can successfully SWITCH its target, and manage to hit the tank out-of-range.

Now you see, my fellow warriors, who is the master of true evilness~~!!!