edit 23 june 2013: below is the original post which may not be accurate anymore, below the quoted text is the information I've posted on the slitherine forum which should be up to date.
As to who shoots first, yes initiative does decide who shoots first.
After the effective iniative has been calculated either the attacker or defender will shoot first.
If the attacker has the highest initiative then it will shoot with his available strength, then it's calculated by using the initiative of both units and some other factors how many units (= dice rolls) of the defender shoot back.
If the defending unit has a higher initiative then it will shoot first and with it's full available (unsurpressed) strenght left. Then after the defender has fired the attacker will shoot back using the same calculation (i.e. 20% doesn't shoot back for every point in initiative the defender has more than the attacker).
You usually want to avoid this, either reduce the defenders unit's strenght and/or supress it with artillery and air attacks.
As to the dice roll that is shown. For every attack a dice roll from 0 to 3 is made. This is a random variable that is used to make the results, well, more random .
So even if you have all the factor's there's still a matter of luck/randomness involved. So even if you attack and you have a initiative of 7 and the enemey has 2 then you don't expect any losses since the enemy will not be able to return fire. However if you roll a 0 and the enemey rolls a 3 then it will defend with 60% of it's strength.
Note that this dice roll is always added last and after the other factors have been used, so for example when attacking a unit in a forest which terrain has a cap for initiative of 2 then a dice roll is made and if that is 2 for example the effective initiative will be 4, so higher than the cap.
And btw, there's still more to be said about initiative since some attacks have special rules, for example when an AT unit is attacking a tank or recon it gets a bonus to it's initiative of 3.
And I'm not sure if I have told that for every unit that you have adjacent (and has not fired yet) to the unit you are going to attack the defending unit will get a -1 penalty for it's initiative.
So when you have 3 unit's adjacent that have not fired yet and you attack with one of those units the defender will get a -2 penalty to it's initiative calculation.
Edit: wrote wrong info, it's correct now (I hope )
This is from the slitherine forum updated with some additional information
The calculations for the Effective Initiative decide two things, the unit with the highest initiative will shoot first - regardless if it's the attacker or the defender - and then, the difference between the initiative of the attacker and defender determines how many units can return fire.
The section below was changed - see the response below from Rudankort
It is not quite like this. Initiative advantage of 4 means that 80% of damage is caused to the enemy before he has a chance to react. In this particular case your attack has caused 3 kills and 1 suppression. From these, 80% are applied upfront:
- 80% from 3 kills is 2.4 kills, rounded to 2.
- 80% from 1 suppression is 0.8 suppression, rounded to 1.
So, a total of 3 points of enemy's strength were disabled before he could shoot back. So he only responded to your attack with 7 points of strength out of 10.
For every point of difference in initiative a unit has over the other unit 20% of the (unsurpressed strength of the) there will be a chance that the other unit will not be able to shoot back.
Therefore if the difference is 5 or more and if the attack causes enough kills and/or surpression the other unit will not shoot back (5 * 20% = 100%).
Fractions are rounded up, so if the a unit is at 4 strength and the difference in initiative is 3 then 60% of 4 will have a chance to not be able return fire, so (1 - 0.6) * 4 = 1.6 and this is rounded up to 2.
Note that if the unit is already (partly) surpressed then only the unsurpressed strength of the unit is used to calculate the amount of units that have a chance to return fire.
This does not apply to artillery versus ground units as defending units cannot return fire ever when being attacked by artillery (even if the artillery unit has a range of 1).
Initiative elements and Effective Initiave
Apart from the attacking and defending unit's base initiave there are many other factors involved, some will add or substract initiative for either or both the attacking and defending unit. There can also be a maximum allowed initiative, a so called cap, due to weather and/or terrain
Weather can cap ininitiave - Rain or Snow caps the initiative at one
Terrain can cap initiative - see the Library.
Note that it's always the terrain of the defending unit that determines any factors regarding any initiative cap.
Any bonus of a hero is added to the calculation
The experience of the unit is partially added to the base of the units intiative, this depends on the type of units attacking.
Initiative bonus for each (full) experience star.
Tank vs Tank 10%
AT vs Tank 5%
Inf vs Tank 0%
Recon vs Tank ?
So if a tank with 4 stars and 9 base initiative attacking another tank it would get 4 * 10% * 9 = 3.6 -> rounded down to 3 added to it's intiative.
Note that the Experience bonus is calculated at the end, the Experience bonus is the shown percentage of the experience and is always rounded down. For example a unit with 10 initiative and 100 experience (equals one star) would usually gain +1 bonus to initiative from experience, however if that unit is attacked by multiple units and therefore gets a -1 penalty from Multiple Attack it's experience would now be 9 and then 10% of 9 would be 0.9 which will be rounded down so effectively it's zero.
If a Tank or Recon attacks an AT unit the AT gets +3 added to it's intiative.
Ambushed/Rugged Defense initiative set to zero (for the ambushed unit or for the attacker against a defender who gained rugged defense)
Multiple attacking units (not artillery - even it has a range of 1) -1 for each unit attacking beyond the first.
No Fuel -2 penalty
A die roll 1-2 is made for both attacker and defender.
This roll is added after the other factors have been determined and the result is always added to the calculated total and is not affected by either weather or terrain cap. Therefore the Effective Iniative can be higher than the cap would allow.
< Message edited by Rood -- 6/23/2013 10:49:51 AM >