This guide contains no claims or information that cannot be extrapolated from the land combat guide.
Please note that this guide frequently converts percents to decimal numbers with the standard conversion that decimal=percent/100 and this conversion will be used without comment in the guide.
This guide assumes some familiarity with the game (e.g. you can navigate the interface and have some idea what unit stats are)
Everyone who has ever read any Victoria II tutorial has undoubtedly seen that they should have as much 
artillery, which fights in the back row, as other units that fight in the front row. They have probably heard claims that artillery is the best unit the game or that it can serve as a force multiplier or any number of other claims that are repeated so often they become dogma. This guide seeks to explain away any mystery around that and make players more knowledgeable about mechanics that greatly influence any Victoria II game. Victoria has a lot of mechanics which can be a little overwhelming, but some, like this, are far more important than others.
The Mechanics
The reason artillery is so much better than every other unit, with the possible late game exception of airplanes, is one completely arbitrary, not intuitive, and, quite frankly, confusing mechanic.
Strength damage inflicted = Base Kills From Roll * (1 + attack / 10) / (1 + Enemy's Tactics / 100)
Where attack is the actual attack stat and is replaced with defense if defending
The part to note is that the damage done is directly proportional to (1+attack/10) which means that a unit with an attack stat of 0 does base damage equivalent to 10 attack points. Or, to put it in simpler terms, every unit in the game basically has 10 more attack and defense than listed.
Example: Players would likely think that increasing a unit's attack from 1 to 2 would double its attacking power, since the attack stat doubles. However, that is not the case, and it actually only increases the unit's attacking power by 12/11 or a little over 9%.
Another mechanic to note is that the support percentage artillery use, which, after the first artillery tech most nations start with, is 200%, multiplies the damage inflicted, not the attack stat. In other words, it multiplies the attack stat + 10, not just the attack stat.
Example: Artillery start the game with 1.5 attack and 200% support for most civilized nations. This means, in the back row, artillery have the attack strength of a unit with 13 attack in the front row, far more than Infantry's starting attack of 5.
Work Shown: (10+1.5)*2 = 23 = 13 + 10 = a unit with 13 attack
The Relevance
These mechanics are extremely relevant towards combat in the game and also should impact tech choices.
Here are tables illustrating how powerful units are attacking and defending at various levels of tech. Note that these assume units with a support stat ( artillery, engineers, planes) are fighting in the back rank.
Attacking and defending power is expressed as a multiple of the power a unit with 0 attack and defense has.
For details of actual unit stats, please see: Land units
Start of Game
All tier-one technologies and inventions
| Name | Attack Power | Defense Power |
|---|---|---|
| Artillery |
2.3 | 2.6 |
 Cavalry |
1.35 | 1.2 |
 Cuirassier |
1.6 | 1.5 |
 Dragoon |
1.5 | 1.4 |
 Hussar |
1.4 | 1.4 |
 Infantry |
1.5 | 1.5 |
 Irregular |
1.25 | 1.3 |
1836
All tier-two technologies and inventions
| Name | Attack Power | Defense Power |
|---|---|---|
| Artillery |
2.94 | 3.5 |
| Cavalry |
1.4 | 1.3 |
| Cuirassier |
1.6 | 1.5 |
| Dragoon |
1.6 | 1.5 |
 Engineer |
0.65 | 1.05 |
| Hussar |
1.4 | 1.5 |
| Infantry |
1.6 | 1.6 |
| Irregular |
1.3 | 1.4 |
1850
All tier-three technologies and inventions
| Name | Attack Power | Defense Power |
|---|---|---|
| Artillery |
3.6 | 4.8 |
| Cavalry |
1.45 | 1.4 |
| Cuirassier |
1.6 | 1.5 |
| Dragoon |
1.7 | 1.7 |
| Engineer |
1.05 | 1.73 |
 Guard |
1.9 | 1.6 |
| Hussar |
1.5 | 1.7 |
| Infantry |
1.7 | 1.8 |
| Irregular |
1.35 | 1.5 |
1870
All tier-four technologies and inventions
| Name | Attack Power | Defense Power |
|---|---|---|
| Artillery |
4.38 | 6.3 |
| Cavalry |
1.5 | 1.6 |
| Cuirassier |
1.6 | 1.7 |
| Dragoon |
1.8 | 2.1 |
| Engineer |
1.5 | 2.9 |
| Guard |
2 | 2.2 |
| Hussar |
1.6 | 2.2 |
| Infantry |
1.8 | 2.4 |
| Irregular |
1.4 | 1.7 |
1900
All tier-five technologies and inventions
| Name | Attack Power | Defense Power |
|---|---|---|
| Artillery |
5.85 | 9 |
| Cavalry |
1.6 | 1.7 |
| Cuirassier |
1.8 | 1.8 |
| Dragoon |
2.0 | 2.1 |
| Engineer |
1.8 | 3.0 |
| Guard |
2.6 | 2.2 |
| Hussar |
1.8 | 2.2 |
| Infantry |
2.4 | 2.4 |
| Irregular |
1.5 | 1.8 |
 Armor |
2.8 | 2.0 |
1919
All tier-six technologies and inventions
| Name | Attack Power | Defense Power |
|---|---|---|
| Artillery |
8.4 | 15.6 |
| Cavalry |
1.7 | 2.1 |
| Cuirassier |
2.0 | 2.2 |
| Dragoon |
2.2 | 2.5 |
| Engineer |
2.2 | 3.4 |
| Guard |
3.2 | 2.6 |
| Hussar |
2.0 | 2.6 |
| Infantry |
3.0 | 2.8 |
| Irregular |
1.6 | 2.2 |
 Airplane |
7.8 | 24 |
| Armor |
2.8 | 2.0 |
This does not include all the reasons players should take into consideration when picking units. For instance, many people prefer Hussars to Dragoons because they have a higher recon stat, which helps with dig in, even though Dragoons would otherwise have better attacking stats.
Also, building all artillery armies isn't advisable, because some units still need to fight in the front row, and Infantry are both better suited for that and cost far less.
Relevance for Tech
One other side effect of this is the small arms tech tree is particularly bad. It is still worth getting because of the combat width reduction and for colonization, but the stat increases it provides to units are somewhat underwhelming.
Take muzzle loaded rifles, for instance. Muzzle loaded rifles increases a variety of unit's attacks by at most 1. Infantry starts with 5 attack, and this tech will raise it to 6. 5 to 6 sounds like a respectable increase: the attack stat goes up by 20%. However, because of the base attack a unit has, this only increases Infantry's power attacking by 16/15 or 6.67 percent.