In Civilization: Beyond Earth, the term "unit" refers to anything that can move around the map. There are a number of different types of units in that could be in play: military units, workers, colonists, trade convoys, orbital units, etc.
Movement Speed is what determines how far you can move during each turn. Some terrain costs more than others, but you can hover over the area with your mouse to see how far each unit can go before you dedicate to any actions.
Combat Strength is the overall power of that unit if it's attacked or attacks another unit directly. All military units have this value. Melee units use their Combat Strength when attacking or defending. Ranged units use their Combat Strength when defending against incoming ranged or melee attacks.
Ranged Combat Strength is used to determine damage when making indirect ranged attacks. It is not used for defensive purposes.
Range is the distance that a ranged unit can attack an enemy; it's measured in hexes. Note that this can be even a single hex. That may sound weird, but it still has a function. Ranged attacks are not countered, so the unit that makes them will not take damage from the enemy that they're attacking. That is why even a one-tile ranged attack is useful! It lets you deal free damage against a target.
Hit Points are a measure of a unit's (or city's) Health. They range from 0 to 100. Some types of damage inflict a flat amount of HP damage; standing in miasma is a good example, as it does 10 damage per turn. Other attacks are based on the ratio between the attacker and the defender and may do as little as 1 damage or as much as 100 damage!
When a unit's Hit Points reach 0, it is destroyed. Health is restored by ending a turn without moving or fighting. This restores 10 Health normally, 20 Health if done inside your territory, or 30 Health if your unit is inside a city. Additional Health may be restored depending on the technological choices that you've made with your civilization.
▣ Bonuses and Penalties in Combat
Units aren't only measured by their Combat Strength. Multiple factors go into determining how hard your people are to kill. Terrain usually protects the defenders (as with forests and hills), though it can expose people to attack, as well (when your people are in marshes).
There are also bonuses granted when your units flank enemies by circling them in on more than one side. This sometimes leads to several bonuses if your units also have traits that give them advantages for being close to other allied units.
Spend time getting to know each of your military units, and find out what gives them the best bonuses before putting them into a large-scale war. If a unit has bonuses when it's not near allies, then use it as a scout and raiding unit, dashing into enemy territory and dealing as much damage as it can.
For units that are meant to go together, form a line. Have your tougher units stand in front, and protect valuable ranged and siege units by placing them in the rear. Watch your sides for flanking attacks by more mobile troops.
▣ Experience Points and Veterancy
Units that attack or defend gain Experience, even if they're fighting against aliens or cities. This Experience (XP) accrues until your unit gains a level of Veterancy. You are then given the chance to heal the unit for 50 Hit Points instantly or to grant that specific unit a bonus to their Combat Strength for the rest of their days. In the middle of a war, it's sometimes better to take the immediate Health so that your experienced unit doesn't simply die off. During more peaceful times, or when you have a chance to retreat and rest, it's better to take the bonus Combat Strength!
- Making a melee attack: 5 XP
- Defending against a melee attack: 4 XP
- Making a ranged attack: 2 XP
- Defending against a ranged attack: 2 XP
Total XP Required
▣ Unit Stacking
As with Civilization V, you cannot stack military units on top of each other. A given tile can only house one land-based military unit and a single non-military unit. This means that you must prepare attacks carefully so that your military doesn't get bottlenecked in a long column that is easily destroyed with ranged fire, city defenses, and orbital bombardment.
Stack good defensive units on top of workers and colonists to protect them from aliens and raiders.
Use lines of melee units to screen against attack, and have your ranged units follow directly behind this line so that they can fire over their allies to assist in warfare.
You can move your units over each other, so long as there is space for the mobile unit to reach the far side of the middle unit. That makes rough terrain especially nasty when you're moving a large group; many troops won't have enough Movement to go through another person and on to the next tile. Thus, you need to get your formation in place before moving into the nasty area.
▣ Unit Categories
There are several categories of units. Knowing the type of unit you're looking at is a quick way to remember what their general use is both on and off of the battlefield.
Melee units are land-based units that can attack enemies in adjacent land hexes. These are usually solid troops that are capable of assaulting areas or defending. They lack Range and Flexibility in their roles but are often the core of your forces.
Ranged units are units that can attack enemies in adjacent hexes and in hexes one or more spaces away by bombardment. Ranged units are often weaker in their total damage output and are almost worthless when attacked directly in melee. However, they are vital in sieges or large field battles because of their ability to fire over allies. This contributes damage against an enemy without sustaining counterattacks. Ranged units are amazing when they're protected by a city or by a screen of melee units.
Naval units move only on water hexes. They cannot enter land hexes, except for coastal cities. They patrol the seas, bombard cities and land units, and fight off the horrors that lurk deep in the ocean.
Air units are airborne craft that provide ranged support to your units by bombing cities and other units. They can also work to interdict enemy aircraft so that you maintain aerial control.
Hover units levitate over the battlefield. They move quickly over any terrain and can even fly over canyons and water tiles. They are some of the most dangerous and flexible raiders in the game. Some of these units are melee attackers and others are ranged, so think of this as a secondary category of unit.
These are weaker units that have little way of defending themselves. Use your military to escort these units around the map, letting them settle cities, improve tiles, and search for special sites. Never leave these units near aliens or enemy units unless you're trying to lure someone into attacking you.
Orbital units are temporary orbiting units. They are deployed on a layer above the battlefield. Each type of orbital provides different bonuses to your Colony. Some enhance cities by adding resources to the tiles underneath them. Others manipulate miasma, and some are battle satellites that attack the ground underneath them.
After an orbital's duration expires, the unit falls from the sky and crashes onto the ground below.
An orbital unit's effect is applied to an area below it, called the effect area or "skirt." For passive effects (say, a Food increase for tiles), this skirt is the area that receives the effect. For activated abilities (for example, a ground bombardment), this is the range where the ability may be used.
Each Affinity has several unique military units. These units are tied to that Affinity, and they have bonuses that are often quite specific (giving them a niche that is exploitable in warfare to get an edge over your opponents).
Often, Affinity units have higher stats than generic units of the same tech level, but they cannot be specialized in as broad a manner. This means that your opponents are going to know what they're facing.
▣ Unit Upgrades
Unit Upgrades are based on Affinity level, rather than Technology, in this version of Civilization. Every Unit has several tiers of Upgrades they may reach, each with a higher Affinity level requirement. Once the necessary level has been reached, the Upgrade becomes available for the player to choose. Upgrades are applied to every unit of that type instantly, rather than on a unit-to-unit basis, without any cost or returning a unit to the player's borders. This causes sudden jumps in military power from time to time, as colonies hit certain Affinity levels and see their armed forces upgrade overnight.
When a Unit reaches a new Upgrade tier, they receive an increase to their base combat or ranged strength. Sometimes this will be accompanied by an additional bonus, such as increased movement speed or extra range. There is also a choice between one of two perks for the Unit, making all Units of that type more specialized.
All generic Units in the game have an extensive upgrade path, with four tiers. The third and fourth tiers are Affinity-specific, requiring you to have a dominant Affinity. Affinity-specific Unit types have only two tiers. These Units are much stronger and have a more specialized role to start with. Their Upgrades allow for hybridized Affinity levels, as well as the Unit's dominant Affinity.
▣ Unit Actions
Most unit actions are self-explanatory, but there are a few tactical uses of these actions that are worth mentioning. Use Alert instead of Fortify if you want to place a unit in an area as a scout. This lets you see if anyone is trying to get through your territory. It's superior for noticing buildups along your borders. Fortify and Alert both provide bonuses to your defenders when they're attacked, so there aren't any downsides to using Alert instead of Fortify. However, using Fortify instead of Alert causes the unit to stay Fortified until the player wakes the unit.
Fortify Until Healed is a great command for restoring units after battle or when they're stopping near home for some rest. Use this so that you don't have to hit the spacebar and skip through all of your wounded units.
Pillage destroys improvements on your current tile. This gets your Colony a small Energy bonus, and it disrupts whatever your rival has in that area. Use this to destroy roads so that enemies can't respond to your invasions as quickly. For the best scenario, have a fast unit race into enemy territory at the beginning of a war, destroy a road that's in rough terrain, and laugh as your opponent bottlenecks all of their responding forces well away from the sight of the actual fighting. Even if you lose your raiding unit in the process, you're going to come out ahead.
Rebase aircraft so that they're always close to the front (whichever front you have, that is). It doesn't take long to reposition your aircraft, so make the most use of them even if you only have a few airborne units. When one war ends, rebase them until they're in position for either defense or your next attack.
▣ Orbital Mechanics
Clicking on the "Orbital View" button opens the Orbital Layer map. This map mirrors the ground below and shows you which tiles are influenced by orbitals that are already deployed. Look for the blue shadow beneath your orbitals to see the tiles in question.
Orbitals cannot be deployed close together. They cannot stack, nor can they share a skirt. Anything that is already influenced by one orbital cannot also be influenced by a second orbital of another type. This prevents you from having all sorts of crazy bonuses by surrounding cities with all of your orbital types.
It's usually very efficient to construct orbitals in one or two cities within your Colony. There are buildings that make orbitals easier to construct, and placing these in all of your cities is wasteful. Also, cities share their total Orbital Coverage. Anything that you launch from your orbital city can be sent to any tile that is within your Orbital Coverage. This allows your orbital city to supply the entire Colony with any effects that it needs for Growth, defense, or whatever else comes up.
Note that most orbitals require a heavy investment of strategic resources (Petroleum and Titanium being the two biggies). If you like using satellites frequently, do your best to secure sites that have these resources and improve them as soon as you can.
Being up in the sky is fairly safe; most units can't attack your orbitals. However, cities and certain special units are able to launch orbital attacks. Don't deploy your satellites directly over enemy artillery or cities unless you really have to; your opponent won't waste much time in shooting your birdies out of the sky.
By the same token, you shouldn't deploy orbitals too close to your rivals' borders. This is a diplomatic gaffe, and it's likely to sour relations with the Colony in question.
Orbitals fall out of the sky when their duration is over, but that's not entirely the end of their journey. You can use crashed satellites for additional resources. Send an explorer to the site in question, and start an expedition. You sometimes recover some cool stuff from these runs! The only cost is that you might have to repair the tile improvements that the orbital crashed into. A minor nuisance, at most.