Unit Healing

[PieceOfMind]

Unit Healing
Last Update: 13/8/2007 (link to Carl Corey's thread)

NEW
Carl Corey has posted some results about the stacking of woodsman III promoted units with medic units. A summary of changes made for the BtS expansion will be given (hopefully) in the not-too-distant future.

The purpose for this article is to comprehensively cover the unit healing feature in Civilization 4 and its various expansions (only Warlords to date). In particular it was written to address frequent questions on the use of medics and how territory affects healing. Many of the important findings are listed in the conclusion.

If you accessed this article through the War Academy, it may be worth checking the associated thread for updates.

Please feel welcome to make suggestions for the article. I especially appreciate more tips for the conclusion.

First, we will need a few key terms throughout:
A friendly civ is a civ with whom you are at peace.
Neutral describes territory which is unclaimed. "No man's land" and "international waters" if you like.
An allied civ is either:
1) a team mate (as defined at game start),
2) a civ with whom you have a permanent alliance, or
3) a master or vassal (Warlords expansion only)

Now, onto unit healing....

If a unit is damaged and eligible for healing, then it will be healed.

Q: When is a unit eligible for healing?
A: Only when it does not perform certain actions which are listed below.

Eligibility for Healing
A unit that performs ANY of the following actions will NOT be eligible for healing:

• Movement*
• Attack
• Pillage
• Bombard
• Load or unload (including from ship to ship)
• Airlift
• Bombing/Air Strike (air units)
• Reconnaissance (air units)
• Re-basing (air units)
• Upgrade
  
  * Units sitting in a moving ship are not considered to be moving.
  

EXCEPTION: The March promotion
A unit with the March promotion is ALWAYS eligible for healing. Any of the above actions which ordinarily disqualify a unit from being allowed to heal instead have no effect. For example, a March-promoted Cavalry can move 1 tile, attack, and then still be eligible for healing.

The following actions will not affect a unit's eligibility for healing:

• Fortify
• Sleep
• Sentry
• Defending against an attacker
• Sitting in the cargo of a ship while it moves
• Accepting a promotion
• Intercept Mission (air units)

In most documentation on unit healing, a unit will be said to heal some "percentage" in a turn. eg. the manual will tell you Medic I heals units on the same tile by 10%. The percent healed is the same as the number of HP healed. eg. A medic will add 10HP to units it heals.

A unit's heal rate is determined by adding its Base Heal Rate to, if applicable, any medic healing, hospital healing and healing from Combat promotions. Details below:

Base Heal Rate
Eligible units will heal:
5HP per turn in enemy territory.
10HP per turn in neutral/friendly territory.
15HP per turn in home/allied territory, OR, in any city which is in resistance.
20HP per turn in any city which is not in resistance.

For your convenience, here's a flow chart for finding the base heal rate in case the above was confusing:



Medics
A unit with the Medic I promotion will heal all eligible units on the same tile by 10HP.
A medic can move and then heal units on the tile it ends its turn on.
A unit with Medic I heals itself if eligible.
A unit with Medic II will heal all eligible units in any adjacent tiles by 10HP. Minor note: a unit with Medic II but not Medic I will NOT heal units on the same tile.
IMPORTANT NOTE: Units with Medic II cannot heal units across a land/sea boundary. Ships in port are considered to be on the land side of the land/sea boundary.

No more than one Medic unit can operate on a unit eligible for healing each turn.
A unit with Medic I and II does not heal units on the same tile any quicker than if it had only Medic I.

Any ships (including transport ships) with Medic I will heal eligible units in their cargo or on the same tile.
A medic unit can heal land, air and naval units.
Medics can heal the units of an allied civ.

Minor note: The Red Cross wonder only gives the Medic I promotion to units which are ordinarily allowed to accept that promotion.

Warlords: In the Warlords expansion, the presence of a great general allows the Medic III Promotion for Medic II promoted units. The Medic III Promotion gives an additional 15HP of healing to units on the same tile and adjacent tiles, totalling 25HP.

Hospitals
A hospital will heal all eligible units on the same tile (city) an additional 10HP.
A hospital can heal land, air and naval units.
A hospital can heal all eligible friendly/allied units.
A hospital does not work in a city during resistance.

Combat IV and Combat V
A unit which has the Combat IV promotion and is eligible for healing will heal itself an additional 10HP only if it is in neutral or friendly territory (this is usually just described as neutral territory).
A unit which has the Combat V promotion and is eligible for healing will heal itself an additional 10HP only if it is in enemy territory.

You'd be forgiven for thinking each of these promotions would give additional healing if in home territory, or in the case of Combat V, neutral territory as well. But in fact this is not true. As an example, consider a unit which has the Combat IV promotion. It will actually heal faster in neutral territory (20HP/turn) than it does in your own territory (15HP/turn). Of course, a home city would match it at 20HP/turn.

Promotion-Heal
Choosing a promotion IMMEDIATELY heals 50% of the HP needed to reach 100HP. If the number of HP needed is odd, the number healed is rounded down. Eg. a unit with 21HP will heal to 21 + (100 - 21) * 0.5 = 60.5 "=" 60HP
A unit need not be eligible for healing to receive the Promotion-Heal.
Accepting promotions has no effect on a unit's eligibilty for healing, and the immediate Promotion-Heal is independent of the healing that happens at the beginning of your turn.



Extra Info

Healing takes place at the beginning of your turn.

If a unit of yours is damaged during another team's turn, your unit will be healed immediately at the start of your turn, so long as it was eligible to do so. For example, fortified units defending a city will heal every turn. This makes it difficult for an attacker to take down a city unless he does it quickly and with sufficient force.

Upgrading a unit does not heal any HP.

AI units and barbarians heal the same way a player's units do. For barbarians, all civs are enemies (for territory considerations).


Healing Formula

There are 4 parameters that affect a unit's healing rate; Base Heal Rate, Medic, Hospital and Combat promotions (IV or V).

Let X be the number of HP a unit has which is eligible for healing.
Let P be the number of HP the eligible unit will heal. Then,

P = min(100 - X, B + M + H + C)

where

B = 5 if in enemy territory
B = 10 if in neutral/friendly territory
B = 15 if in home/allied territory, OR, in a city in resistance
B = 20 if in a city which is not in resistance

M = 10 if a medic is available to operate on the unit (In Warlords, if the medic is Medic III then M = 25)
M = 0 otherwise

H = 10 if the unit is in a city with a hospital
H = 0 otherwise

C = 10 if the unit has Combat IV and is in neutral (or friendly civ's) territory
C = 10 if the unit has Combat V and is in enemy territory
C = 0 otherwise

A unit with X hit points which is eligible for healing will heal to X + P hit points at the beginning of the next turn.

Let N be the number of turns required to heal a unit. Then,

N = ceiling[(100 - X) / (B + M + H + C)]

Note the formula always holds because B + M + H + C is never 0, and 0 < X =< 100.

N is the same as the number of turns the game will display for a unit to heal completely. Minor note: Units that are not eligible for healing will still display the same N so actually they will take N+1 turns to heal.

For those interested, the Promotion-Heal has the following (obvious) formula.
Let X be the HP of ANY unit which has a new promotion available. Selecting a promotion will IMMEDIATELY heal P hit points where

P = floor[(100 - X) * 0.5]

A unit will therefore have X + floor[(100 - X) * 0.5] hit points immediately after choosing a promotion.



Conclusion

• A unit in enemy territory will take 20 turns to heal if it has less than 5HP. This is the maximum number of turns a unit could take to heal.
• A unit in enemey territory will heal 3 times faster if he has a medic available. He will heal in 7 turns at the most, at a rate of 15HP per turn (as opposed to 5HP per turn without a medic).
• A unit without Combat IV will heal fastest in a home or friendly city, with a hospital and a medic of your own or ally's (40HP per turn and maximum 3 turns to completely heal).
• A unit with Combat IV will heal faster in a friendly civ's city than a city of your own! Also, it will heal faster in neutral territory than in your own! I found this surprising.
• For interest's sake, the fastest any unit can heal is 50HP per turn*. The unit must have Combat IV and be in a friendly civ's city that has a hospital and a medic of yours or your ally's. With this set up you will have a maximum heal time of 2 turns! 20HP from being in city, 10HP from medic, 10HP from hospital and 10HP from Combat IV. Total: 50HP
  *With Warlords, a medic III unit would allow a max heal rate of 65HP/turn!
• March is generally a useless promotion for your medic units. It is often confused but you should give March to units which you will want to BE healed. For example, send along a Medic I Explorer with your Mech Infantry or March-promoted units and you will have a force which heals quickly when on the move even in enemy territory.
• If you have damaged units in a friendly civ's territory, put them in one of the civ's cities. These cities are just as good as your own cities at healing your units!
• Armored units and helicopters cannot be given Medic promotions. Armored units, helicopters and naval units cannot be given the March promotion. However, these promotions can be retained through unit upgrades eg. by upgrading march promoted cavalry to gunships.
• Often it is wise to hold off on promoting a unit so that after a battle the immediate (and significant) Promotion-Heal can be used.

[PieceOfMind]

Another article has been written on Unit Healing by ModernKnight, found here.
While most of the material is covered in the present article, he has some useful tips to add.

Originally Posted by ModernKnight

Healing can take up to 20 turns for a near-dead unit in enemy territory without a medic, but this would only take 6-7 turns (1/15%) with a medic. The quickest a unit near death can be healed is 4 turns (friendly city with medic; 1/30% rounded up), although 3 turns max is more realistic. (And certain if you're lucky enough to have a hospital.)

These numbers dictate that if you have a medic in enemy territory (15%), you should not move to be healed at a 30%+ city unless you can get there in ONE turn. Why?

• It takes 6 turns staying where you are. (Or just barely 7 if near dead.)
• It takes 3 turns at a 30%+ city (with medic or hospital).
• The difference is 3 turns.
• If it takes two turns to get to the city, it would take 2 to get back. Total: 4 turns.
• Or even if you can make it there and back in 3 (changing position), there has been no net gain - you're healed (and back or whatever) in 6 turns. Why not just stay there and get your fortify bonus?

[DaviddesJ]

Originally Posted by PieceOfMind

Minor note: a unit with Medic II but not Medic I will NOT heal units on the same tile.

You can't get Medic II without Medic I, right? Except with the editor, or perhaps a mod.

[PieceOfMind]

Originally Posted by DaviddesJ

You can't get Medic II without Medic I, right? Except with the editor, or perhaps a mod.

That's correct. Using the world builder you can give a unit Medic II without Medic I and it won't heal units on the same tile. It might be important for someone to know.

[Roland Johansen]

Good article.


I didn't see any mentioning of the healing bonuses from the last two combat promotions. They're not that important, but you seem to want to be complete, so...

A very minor detail: are units that were just promoted elligible for healing that turn? I wouldn't think so, but none of my units were ever in that situation.

I don't know the answers for your questions, but they should be easy to find with the worldbuilder, I think.

[PieceOfMind]

Originally Posted by Roland Johansen

Good article.


I didn't see any mentioning of the healing bonuses from the last two combat promotions. They're not that important, but you seem to want to be complete, so...

A very minor detail: are units that were just promoted elligible for healing that turn? I wouldn't think so, but none of my units were ever in that situation.

I don't know the answers for your questions, but they should be easy to find with the worldbuilder, I think.

Thanks for the comments. All of them will be taken on board. I'll do some tests.

As for the combat promotions I completely forgot about those - I rarely use them.

EDIT Changes have been made to the article in response to your comments

[Qitai]

Originally Posted by PieceOfMind

-March is generally a useless promotion for your medic units. It is often confused but you should give March to units which you will want to BE healed. For example, send along a Medic I Explorer with your Mech Infantry or March I Tanks and you will have a force which heals quickly when on the move even in enemy territory.

Thanks for the very useful article.

For the above statement, does it mean that the medic will always work base on the square which it ends it's turn on. And it does not matter if it has moved at all. Also, would an injured unit which has move benefit from the medic?

Let's use an example to elaborate this.

A injure medic and two other injured unit axeman on the same tile in enemy territory. One axeman has not moved and thus is eligible for healing. The other has moved to the same tile.

So, which and how much does each of them heal?

Injured axeman who has not moved : 5 + 10 = 15HP?
Injured axeman who has moved : 0HP or 10HP?
Inijured Medic who has also moved : 0HP or 10HP?

Thanks

[PieceOfMind]

Qitai,

It does not matter whether your medic moves or not unless you need to heal the medic itself. You can move a medic and then heal a unit. Note the movement of a unit only affects its eligibility to BE healed, not whether it can heal something else.

The medic heals the units it ends its turn on. Correct (assuming the unit is eligible for healing).

An injured unit which has moved would not benefit from the medic because it would not be eligible (keyword in the article) to be healed.

For your example,
Injured axeman who has not moved : 5 + 10 = 15HP (correct, 5 from territory and 10 from medic healing)
Injured axeman who has moved : 0HP (it moved so it is not eligible for any healing)
Inijured Medic who has also moved : 0HP (again because it is not eligible for healing due to moving)

[apdavis828]

the only thing i know about healing is that it sucks... it takes forever no matter which unit i'm healing or where it is.

[Sahkuhnder]

Excellent article. Thanks for your efforts.

[Qitai]

Originally Posted by PieceOfMind

Qitai,

It does not matter whether your medic moves or not unless you need to heal the medic itself. You can move a medic and then heal a unit. Note the movement of a unit only affects its eligibility to BE healed, not whether it can heal something else.

The medic heals the units it ends its turn on. Correct (assuming the unit is eligible for healing).

An injured unit which has moved would not benefit from the medic because it would not be eligible (keyword in the article) to be healed.

For your example,
Injured axeman who has not moved : 5 + 10 = 15HP (correct, 5 from territory and 10 from medic healing)
Injured axeman who has moved : 0HP (it moved so it is not eligible for any healing)
Inijured Medic who has also moved : 0HP (again because it is not eligible for healing due to moving)

Thanks. These are very usefu information.

[Roland Johansen]

Originally Posted by PieceOfMind

Thanks for the comments. All of them will be taken on board. I'll do some tests.

As for the combat promotions I completely forgot about those - I rarely use them.

EDIT Changes have been made to the article in response to your comments

Ah, good to see that you found the answers to your questions. Strange that a combat IV unit will heal faster in neutral territory then in your own territory. I would have expected that the game considers your own territory at least as good as neutral territory. It's not that important but still rather strange.

I just noticed that I asked the wrong question.

I asked:
"are units that were just promoted elligible for healing that turn? I wouldn't think so, but none of my units were ever in that situation."
while I wanted to ask:
are units that were just upgraded elligible for healing that turn? I wouldn't think so, but none of my units were ever in that situation.

Do you know the answer?

Thanks in advance.

[PieceOfMind]

Roland,

I haven't checked but I'm guessing they won't be eligible if they've just been upgraded - since the upgrade changes a unit's "dot" to red it probably is equivalent to making a move. I'll check tomorrow.

EDIT The article was updated and 'Upgrade' added to the list of ineligibility conditions

[Wreck]

Originally Posted by PieceOfMind

A unit is eligible for healing if it has not moved at all in its turn. That is it forfeits its move so that it can be 'healed'.
A unit that is eligible for healing will be healed at the beginning of the next turn, after all other AIs/players/barbarians have moved. For completeness, only a damaged unit can be 'healed'.

A unit with the March promotion is always eligible for healing, with no exceptions.
A unit which loads/unloads in its turn is not eligible for healing. This includes loading from ship to ship.
A unit which spends its entire turn in the cargo of a ship (no unloading/loading) is eligible for healing.
A unit which is airlifted in its turn is not eligible for healing.
A unit which is attacked is eligible for healing, so long as it does not move from its position in its turn.
A unit which attacks, pillages or bombards during its turn is not eligible for healing.
Air units are eligible for healing if they do not re-base or carry out any missions for their turn, with the exception of the Intercept mission - A unit on an Intercept mission is eligible for healing.

This is a bit unclear. Is a unit with March able to attack, load/unload, be airlifted, etc. and heal? If so, then what you wrote is right - "always eligible" - but I'd prefer it not to be in the list of things qualifying what is "moving".

Also, "if it has not moved at all in its turn" is not really consistent with the ability to be moved in a transport.

One more very minor nitpick: you don't need to bold "eligible" initially because you are not using it in a non-standard way.

That is, I'd rewrite this as:

Originally Posted by me

A unit will only heal if it is damaged, and if it is eligible for healing. Units with the March promotion are always eligible for healing, regardless of what they do during their turn.

Units without March are only eligible for healing if they don't do anything during their turn, except standing still (fortifying is allowed, as is Intercept for air units), or spending the entire turn in a transport (regardless of whether the transport moves). Being attacked does not affect a unit's eligibility to heal. Actions which will make a unit without March ineligible to heal include:

• attacking
• bombing
• bombarding
• pillaging
• being airlifted
• loading onto a transport, or between transports
• unloading from a transport
• rebasing
• reconnaissance

A unit that is eligible for healing will be healed at the beginning of the next turn, after all other AIs/players/barbarians have moved.

[PieceOfMind]

It is a bit unclear. Sorry about that.

What you thought was a list of what counts as moving I thought of as a list of "eligibility or not" conditions. That's not important though.

I bolded eligible the first time I used it because it was essentially a definition. If readers wondered what exactly being eligible meant while reading somewhere else in the article, they could refer to that first definition.

I'll re-word it a bit to try and make it clearer. I'll use part of your suggested re-wording.

Your suggested re-wording isn't exactly what I want to write because I want units with March to be the exception, rather than units without march to be the exception, because there will be more units on the battlefield without March.

EDIT The article has been updated with your comments in mind. Thanks Wreck

[Zombie69]

I already figured all this by myself except that i thought healing was 20 HP in your territory, city or not. For this information alone, this was worth the read.

Very good article!

[PopTarts]

I could've sworn that a few times, Barbarians seemed to heal while moving. It was moving towards my city but on every turn it became stronger. I also remember a Barbarian Axeman that took my city that had more HP the next turn when I tried to take it back. Anyone else notice this?

[Roland Johansen]

Originally Posted by PopTarts

I could've sworn that a few times, Barbarians seemed to heal while moving. It was moving towards my city but on every turn it became stronger. I also remember a Barbarian Axeman that took my city that had more HP the next turn when I tried to take it back. Anyone else notice this?

Probably the axemen in your examples got promoted. When units are promoted, they get half of the lost hitpoints back. This is also mentioned in the article.

[S.ilver]

Excellent useful article! Although I you need your units to still be alive to heal them, so I guess I need to work on that

[KillerCardinal]

Originally Posted by Roland Johansen

Probably the axemen in your examples got promoted. When units are promoted, they get half of the lost hitpoints back. This is also mentioned in the article.

Nope, I actually observed this one time. There was a barbarian archer that I almost managed to kill(but not quite). It went down to .5 strength. Next turn, it jumped up to 1.7 strength next turn due to the promotion. Then next turn it healed again. EACH turn, it did something(either pillaging or moving). I mainly noticed this because I was planning on doing one of two things:
1) the turn(or two) of inactivity for it to heal, so I could produce a better defender;
2) it keeping on coming, but damaged at least.

Now when it got to my doorstep fully healed faster than I expected I said "WTF!" , and reloaded the autosave and watched it advance.

So unless I was really out of it, that was NOT due to the promotion.