For analysis of these combat rules, including the tricks they induce, see the article How to Win Battles.
Types of Combat
In EU2, there are three kinds of combat: normal land combat, naval combat, and assaults (land units attacking a fortified city). Although land and naval tech are distinct, and there are a few special rules related to each kind of combat, they are all resolved the same general way.
Combat alternates between two modes of attack methods: fire, and shock. The time when a particular mode is active is called a "phase"; thus there are the "fire phase" and the "shock phase". You can tell which phase is currently active in a battle involving your own forces by selecting any of them. The battle screen is displayed; on it you'll see a little "fire" icon in the fire phase, and a "shock" icon in the shock phase.
Although they are resolved similarly in the abstract, fire and shock tend to have very different effects from each other, especially at lower tech levels. Fire tends to inflict mostly morale damage, while shock actually kills men. When a battle starts, the first phase is a fire phase. Then comes a shock phase, a second fire phase, a second shock phase, etc., repeatedly, until the battle ends.
Because all military units have shockpower, there is always a shock phase in every battle if it goes on long enough. But not all units have firepower. There will be fire phases in combat only if some military unit on either side has non-zero firepower. If all units currently present in combat have no firepower, fire phases are skipped.
Each phase lasts five days. Each side in the battle gets a new virtual die roll at the start of each phase. This die roll lasts through the phase; it determines the damage inflicted during the phase. Damage is inflicted daily, with one-fifth of the damage indicated by the CRT inflicted for each day of battle except for the first phase. Because there is no damage inflicted the first day of battle, damage of the first phase is spread equally among the next four days.
There may also be a "routing phase" beginning on any random day of a shock phase. A routing phase can only occur in land battles in a plains or desert province. The side doing the routing must have at least four times the shock power of the opposition. The shock stat of the leader is of importance in computing the relative shock power. Manoeuver may also be of importance in computing the damage of the routing phase. When a routing phase begins, extra very high damage is assigned to the routed opponent. The routing phase lasts until the shock phase would normally end.
At the end of battle, there is a "flight phase" that lasts only the day that battle ends. Additional damage may be assigned to the losing or fleeing army. The amount of damage depends on relative shock power of remaining armies on the day battle ends. Also, manoeuver is very important. In fact, an army that retreats before morale breaks can only receive damage from the flight phase if the maneouver of the winner is higher than that of the army that flees.
Here is the process by which a die roll, and the forces involved in a battle (and their owning countries' tech levels) determine damage.
Although both forces get to simultaneously inflict damage on each other, we can analyze the process by which damage is determined one way at a time. For this purpose it is useful to call one force the "inflicting" force, and the other, the "receiving" force. The inflicting force inflicts damage; the receiving side is damaged.
For die-roll modifiers, it is also important to understand the concepts of a battle's attacker and defender. The attacking force is the force that moved into the province or sea zone, thus triggering the battle. The defending force is the other force. Other forces can enter the battle after it starts, on either side, without changing the attacker/defender.
Determining CRT Column
First, the tech levels of the two countries are compared, in order to determine which CRT column will be used by the inflicting force. There are five CRT columns: A, B, C, D, and E. A is the best; E is the worst. The lookup is simple enough: use both sides' relevant military tech field (land technology for land battle or assault, naval technology for naval battle) in the following tables. The inflicting side's tech determines the row; the receiving side's tech chooses the column.
Land Fire CRT Column Determination
tech 0-8 9-13 14-17 18-25 26-34 35-50 51-60 0-8 E E E E E E E 9-13 C C C D E E E 14-17 B B C D E E E 18-25 A B B C D E E 26-34 A B B B B D D 35-50 A A A B B C C 51-60 A A A A A B B
Land Shock CRT Column Determination
tech 0-8 9-13 14-17 18-25 26-34 35-50 51-60 0-8 A B B C C D E 9-13 A A B C D E E 14-17 A A B C D E E 18-25 A A B B D E E 26-34 A A A B B C D 35-50 A A A A B C C 51-60 A A A A A B B
Determining Die Roll Modifier
Next, we add up the die roll modifiers, that is, the bonuses and maluses that the inflicting force has to their die roll on the CRT. Their sum is the "net DRM", or usually just "DRM". For the most part, the DRMs are determined by things that don't change in the battle; the net DRM currently being used (except, possibly, for morale effects) is shown on the battle screen next to the fire phase indicator.
Here are the DRMs:
- Inflicting leader bonus: the inflicting force's leader's statistic for the relevant phase is added.
- Receiving leader malus: the receiving force's leader's statistic for the relevant phase is subtracted.
- Attacking across water: -1, if the inflicting force is the attacker, and it entered the battle province:
- across a river
- across a strait
- moving ashore from a sea zone
- unloading from a fleet in a port
- Defending across water: +1, if the inflicting force is the defender, and the attacker attacked across water (as per above).
- Defending in mountains: +1, if the inflicting force is the defender, and the terrain in the province is mountains.
- Cavalry bonus: +1, if the inflicting force has at least twice as many cavalry as the receiving force, and the terrain is plains or desert. In this case you'll see a little white "horse head" icon on the battle screen, below the force which has this advantage.
- National waters: +1, for a naval fight in the national waters of the inflicting force
- National waters: -1, for a naval fight in the national waters of the receiving force
- Morale: although this is not certain, it appears pretty likely that a force that is low on its morale (relative to the enemy, or perhaps its own maximum) fights poorly.
The Die Roll
No dice are actually rolled. Rather, a virtual 10-sided die is virtually rolled, which results in a random number from 1 to 10.
Lookup in the Combat Results Table
With the relevant CRT column in hand, and die roll modifier, and the die roll, we can now look up the result in the CRT. This is straightforward. Rolls less than 0, or greater than 16, are treated as 0 or 16 respectively.
A B C D E 0 0/0 0/0 0/0 0/0 0/0 1 0/0.10 0/0.10 0/0.10 0/0.01 0/0.01 2 1/0.10 1/0.10 1/0.10 1/0.05 1/0.05 3 2/0.25 2/0.25 2/0.25 2/0.10 1/0.10 4 5/0.25 2/0.25 2/0.25 2/0.25 2/0.15 5 5/0.50 5/0.50 5/0.50 5/0.25 2/0.25 6 10/0.50 10/0.50 5/0.50 5/0.50 5/0.25 7 15/1.00 10/1.00 5/1.00 5/0.50 5/0.50 8 20/1.00 15/1.00 10/1.00 10/1.00 10/0.50 9 25/2.00 20/1.00 15/1.00 15/1.00 10/1.00 10 30/2.00 25/2.00 20/2.00 20/1.00 15/1.00 11 35/2.00 30/2.00 20/2.00 20/2.00 20/1.00 12 40/2.00 35/2.00 30/2.00 25/2.00 20/2.00 13 45/3.00 40/3.00 35/3.00 30/3.00 30/2.00 14 50/3.00 45/3.00 40/3.00 35/3.00 30/3.00 15 60/3.00 50/3.00 45/3.00 40/3.00 35/3.00 16 60/4.00 55/3.00 50/3.00 45/3.00 40/3.00
The first number in the result (before the "/") is the percentage of the inflicting force's power rating which will be subtracted from the receiving forces as casualties. The second number in the result (after the "/") is the loss in morale for the receiving force.
For example, if the inflicting force gets to roll using column B, and gets 12 after modification, the receiving force will have as casualties 35% of the inflicting force's power rating, and will lose 2.00 from its morale. These losses will be pro rated into fifths and applied over the five days of the current phase. After the passage of five days, a new phase will start, with new rolls for both sides.
The result of the CRT is two numbers, a "power rating" multiplier which determines casualties, and an amount of morale. Applying the morale damage is straightforward: if a loss of morale of N points is indicated, then N/5 points are subtracted from the receiving forces' morale level for each day of battle. If the resulting morale hits zero, then that side immediately loses the battle, and all surviving forces are forced to retreat.
The power rating multiplier application is more complicated. To understand it, first we must understand the combat power that a military force has. Each force has a net firepower rating, which is the combined firepower of all units on the side. Similarly it has a net shockpower rating. This rating is simply the sum of the ratings of all armies/navies on the side. The rating of each unit is its size, times its "power rating", and possibly halved for terrain.
The size of a unit is computed in army units. The power ratings are determined by the unit type and technology, and can be found in the land tech table, or the naval tech table. Modifiers for terrain are as follows:
- in forest and mountains, attacking cavalry have halved shockpower
- in swamp, all units have halved firepower and shockpower
As with morale, casualty application happens over five days. If N army units of damage is indicated, then N/5 army units of the receiving force are killed for each day of battle. Note that the amount killed are determined by the strength level of the inflicting force as it was at the start of the phase: even though it takes damage over the five days, it keeps inflicting damage as it was at the start.
Example: in the land tech table we find that at land tech 1, a cavalry unit has no firepower, and 400/1000 shockpower per army unit. Thus, a cavalry army of 8200 men, which is 8.2 army units, has 3.28 shockpower. If it inflicts 35% of that as casualties, that is 1.148 army units, that is, 1148 men. (You can see in this example how a smaller force might be killed in just a few days.)
Here's another example: the same thing, except it's an 8200 man infantry army. This army also has no firepower at tech 1, but it only gets 50/1000 shockpower per army unit. So it has a total of .41 shockpower. If it gets the same roll, it inflicts .1435 army units of casualties.
If there are multiple armies present on the receiving side, the total damage inflicted is portioned to each one proportionate to its size. To a specific army, damage is not inflicted evenly if it has multiple unit types (i.e. it mixes infantry and cavalry). Casualties are inflicted disproportionately on infantry, then cavalry, and finally artillery. This process uses the same proportions as attrition (5/6 of casualties to infantry, 1/6 to cavalry).