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.