A unit in Civilization V is a mobile entity which can move around the map and perform certain functions. Most units in the game are military (combat) units - they have the ability to attack and damage other units and cities. Those that can't do that are also known as civilian units.
Units are the "mobile" part of your empire, just as cities are its "stationary" part. Civilian units are essential to its economy, while military units ensure its safety and allow you to attack and defeat other empires.
Types of Units
- Civilian units are those that have no immediate military use (can't attack). However, this doesn't mean they aren't important - on the contrary! They perform a wide range of useful activities, from constructing improvements to founding cities. Civilian units are often expended after performing their duties, especially if they are Great People. Also, all civilian units can be instantly destroyed, or even captured by the weakest enemy military unit which moves into their tile.
There are several types of military units, which are often referred to in other articles:
- Land units. These are all units which are designed to act on land. Once the Optics technology is researched, they can enter water tiles through the process of Embarkation. While embarked, land units use transport ships to move across water. In this state they can't attack (unless they attack a land tile), and are themselves very vulnerable to attack. Certain abilities can diminish this vulnerability.
- Naval units or Ships. These are the units native to water tiles. They can only be built in coastal cities, and can only move on water tiles. Ranged naval units may attack units on the land, though.
- Melee units. All those units which can only attack in melee — that is, units in tiles adjacent to them. They can be both land and naval. See also Melee combat.
- Archery or Ranged units. All those units that have ranged attack capabilities (usually can fire on units from several squares distance, and don't suffer counterattack from melee units). They can be both land and naval. See also Ranged combat.
- Siege units or weapons. These are land units specifically designed to attack cities. All of them have an attack bonus against cities, except for the Hwach'a.
- Mounted units. These are highly mobile land units, specializing in hit-and-run attacks. A common trait of theirs is the ability to move after attacking.
- Gunpowder units. These are middle and late-game land units, armed with guns. They are essentially modern melee units, replacing the melee units of earlier eras.
- Armored units. Late-game mobile land units. They are the practical successors of mounted units.
- Air units. These are late-game units that are able to fly. These units are essentially melee units which are able to move through the air. See also Air combat.
- Bomb units. These are powerful late-game units. They explode when used to attack, meaning that they can only be used once.
There are several ways to get units:
- By training/producing them in a city. This is the straightforward way - just set the Production cycle of an applicable city to the unit you want, and after several turns the unit will appear in the city. Note that military units may start already with experience if trained in a city with the relevant buildings - this will allow them to get one or more promotions and exit the training stage more dangerous than normal units!
- By purchasing them with Gold in a city. This can be done again in applicable cities, and if your treasury has the necessary currency available. Usually this is Gold, but certain units may only be purchased with Faith; also, certain religious beliefs vastly extend the list of units which may be purchased with Faith, allowing additional flexibility. The purchased unit appears immediately in the city, and may again gain experience, if the relevant buildings are present. Note that you can't purchase units of a class which is already present in the city - for example, if there's a military unit stationed there, you'll have to take it out to purchase another one.
- By generating enough of the relevant Great People points. (Only applies to Great People.) These points are generated on a per-city basis, and the relevant Great Person will be "birthed" in this city. Exceptions to this rule are the Great General, Great Admiral, and Great Prophet. Their points generate globally, not locally, and they are "birthed" in random cities (for the General and Admiral) or in the capital/holy city (for the Prophet).
- By being Friends or Allies with a City-State. In this case the gifted unit will appear in your territory, close to the City-State which gave the gift. Units gained thus sometimes also come with experience, which varies depending on the number of military training buildings the City-State has constructed (and is increased by the unique ability of the Siamese). Usually only Militaristic City-States gift units. The gifts are always era-relevant, meaning that you won't get an Archer if you're in the Renaissance Era; you'll get a Crossbowman instead. Also note that all Militaristic City-States have a "special" unique unit they are able to gift - you'll start getting it during the era this unit normally appears (and only during this era!) if you happen to be their ally at the time. Finally, note that all City-States will start gifting Great People if you complete the Patronage Social Policy tree. Gifted Great People are random.
- By building Wonders. Several Wonders in the game have the effect of supplying free units at completion - for example, completing the Pyramids gives you two Workers, while completing Broadway gives you a free Great Musician. Units gained this way only appear once, meaning that if an enemy later conquers the city with this Wonder, they won't get the free units again.
In some cases, you will also need strategic resources for your units. Any resources needed are deducted from the total at the beginning of the Production cycle for the relevant unit, or at the moment of its purchase. If you have no available counts of the needed resource, you won't able to build or purchase this unit! You should also note that if you had produced a unit which needs a particular strategic resource, and later lose access to this resource so that its count drops to negative values, this unit (and all that need this resource) will fight with a -50% Combat Strength penalty until you rectify the situation!
Unit Supply and Maintenance
Each empire can only support so many units - this depends on the number of cities and Population per city. Also, once produced, each unit costs Gold to maintain, with the cost going up in successive eras for more advanced units. In fact, unit maintenance is one of the two big stones weighing down your empire's treasury (the other one being building maintenance). Maintaining a large army can be quite a financial challenge, especially in the late game, so think carefully about whether or not you need all those Workers and Inquisitors lying around doing nothing.
Note that if your Gold output becomes negative and your treasury empties, your units may start disbanding (vanishing) on their own! So, if you don't want to lose the army you've trained and honed so carefully, take care to have enough Gold at all times!
Unit Statistics and Abilities
All civilian units have certain special abilities. Some of them are inherent to the unit, such as the "Found City" ability of the Settler; others (most of the abilities of the Worker) are unlocked via technological advancement.
Military units have a number of statistics which control their core performance and abilities in combat (you can check them here). They also may have special abilities, although these are quite focused and with limited use (such as bonuses against certain unit types). However, all military units may also gain promotions by gathering combat experience and advancing in levels. These promotions may give them special abilities which make them really fearsome in combat. For a list of promotions, check here, and for the mechanics of gaining experience and leveling up, check here.
This refers solely to military units, and means the process of replacing outdated weaponry and machines with more modern ones. You will notice that despite the huge number of units available in the game, most of them actually fall into several distinct types (see above), which simply change weapons and equipment (and tactical formations) during the ages. This change is known as unit upgrading, and may be done only after you research certain key technologies (developing the new, more advanced unit, and allowing the upgrade). The unit needs to be inside your territory (no, Allied territory is not applicable in this case!), and you'll need to spend some Gold on the upgrade. Air units may only be upgraded while in cities - carriers can't support the high-tech engineering needed for the upgrades. The unit loses all its remaining Movement Points for the turn of the upgrade, and is ready to go the next turn. Also, if the unit was wounded, it will continue at its present Health even if it did not move at all on the turn of the upgrade.
Maybe the greatest advantage of upgrading units is that they retain all their promotions, and even some of their inherent special abilities. Core abilities like extra strength or mobility are usually lost, while "special" abilities and promotions like "Great Generals" or "Extra Range" are retained. So, for example, when you upgrade an Aztec Jaguar to a next-gen Swordsman, the new Swordsman will not only retain all promotions the Jaguar had earned during its existence, but it will also retain the Jaguar's Woodsman abilities! Note that some civilizations' unique units come with free "regular" promotion (such as Drill I or Siege I). These units are spawned with these promotions, or acquire them automatically upon upgrading from previous units. You should be aware of that and plan not to waste experience for a promotion you are about to get for free later!
Upgrading existing units is much more advantageous than producing new ones, not only because of previously-earned abilities that are retained, but also because you save the Production time for building the new units in your cities. Of course, you'll need to ensure you have enough Gold for the upgrade, as well as any strategic resources needed.
Some common upgrade costs on standard speed include:
Warrior -> Swordsmen (80 gold)
Spearmen -> Pikemen (75? gold)
Archer -> Composite Bow (80? gold)
Composite Bow -> Crossbowman (100 gold)
Chariot Archer -> Knight (130? gold)
Horsemen -> Knight (90? gold)