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The Research Screen[edit]

The HOI III Research Screen
  1. locked slider; will not move if you move other sliders; will move if #2 changes; right-click to unlock
  2. total leadership you've; hover to see base leadership and modifiers
  3. theory; hover to see type
  4. practical; hover to see type
  5. value of the theory/practical on the left; the higher the number, the faster anything depending on it performs
  6. combat practicals; unlike all other icons, these are gained primarily by performing combat; hover to see type
  7. category of the theory/practical inside; only visual impact
  8. technology
  9. shows the level to be researched next; in this case the current completed level is 3
  10. ai mode; normal means everything is controlled manually; research ai everything by the ai; slider ai only the sliders
  11. historical year of the tech to be researched next; everything ahead gives a malus, though you won't get a bonus if you're behind
  12. if that tech is researched, you'll gain 1 in that theory/practical
  13. that's a theory/practical influencing the research
  14. current research; green means there's current progress; red not; canceling a tech doesn't kill the progress already made
  15. slider; set the amount of leadership you'd like to use for that field
  16. slider position
  17. tech category; only visual impact
  18. Difficulty (red, yellow, or green).; influences research cost; higher number, higher cost. Default research time for the techs is 12.5*number+125 days. Thus, for difficulty 1, it would be 137.5 or 138 days. Then, your knowledge levels in theory and practicals relevant to the techs are applied, as well as your research efficiency
  19. one-shot tech; has only one level; typically enables a specific unit or base invention

Research Time[edit]

The time to research a tech is given by the following:

 research time = 125 days * (100% + difficulty level * 10%) * (100% + 150% for each year ahead of historical year) * (100% - skill modifier) / (100% + other research speed modifiers)

Research Modifiers[edit]

  • Researching Ahead of Historical Date: Each year ahead of the historical year increases the research time by 150%. This is calculated by year only; e.g., researching a 1937 tech in 1936 is one year ahead no matter if it is January 1 or December 31. There is no bonus for researching behind the historical date.
  • Espionage: Enemy spies may decrease research speed. If this is the case, the penalty will show up in the tooltip for techs being researched.
  • Research Technologies: The computing machine technologies reduce the time needed to research a new technology. The Mechanical Computing Machine techs reduce the time by 2% each, while the Electronic Computing Machine techs reduce it by 5% each.

Practical knowledge is a concept that represents the nation's experience in engineering and construction of each particular field. Increasing practical knowledge is done only through production. Otherwise, practical knowledge will decay over time. Practical knowledge has two effects in game:

  • Modify research time (for technology that depends on practical knowledge)
  • Modify the time it takes to produce units

Effects on Production[edit]

Practical knowledge affects the time and cost of producing things. It is not a linear function; that is, having a practical of 50 does not reduce building time and cost by 50%. It is approximately defined by a piecewise linear function with the following segments:

From To Bonus per practical
Practical Bonus Practical Bonus
0 -50% 5 0% 10.00%
5 0% 6 5% 5.00%
6 6.25% 13 15% 1.25%
13 14.2% 25 ~23.3% ~0.8%
25 ~23.3% 90 48.8% ~0.4%
90 ~46.4% 99 48.6% ~0.2%

The chart below illustrates the effect of practical on production.


An approximate fit would be:

  • Linear regime (below 5 Practical): +10% time and IC per point below 5.
  • Square root regime (above 5 Practical): Time and IC reduction of 5% * sqrt(Practical - 5).

Therefore, a practical value of 0 means that the time and IC cost to produce something increases by 50%. Meanwhile, a practical value of 10 creates an ~11% reduction in the time and IC cost.

Practical Knowledge Table[edit]

By taking a quick look at the table, one can see that the game designers intended for most costs to be around 1,000 IC-days per practical. For those fields that do not fit this norm, one can see that the designers strove for all units in that category to have the same cost. Some fields, due either to low cost across the board or to low cost in a single unit, are easier to acquire experience in.

The easiest fields are Militia and Rocket, being about half of the 1,000 IC-days baseline cost. Massive construction of Flying Bombs and Garrisons will lead to an enormous explosion of practical, quickly cutting production time and cost. Rocket Artillery is also a relatively cheap way of increasing Artillery Practical, being significantly cheaper than the next cheapest artillery unit in terms of IC-days per practical. Interceptor squadrons are the quickest way to increasing Light Aircraft practical. Motorised Infantry is somewhat cheaper than the next most costly unit in the Mobile Unit field. Aside from these few examples, all other fields are relatively balanced.

Unit/Building Type Cost in IC-days Practical Type
Armor 1,005.9 Armor
H-Armor 1,008 Armor
SH-Armor 1,088.89 Armor
Light-Armor 1,008 Armor
Rocket Artillery 845.5 Artillery
Artillery Brigade 1,000 Artillery
AT 1,000 Artillery
AA (brigade) 1,106.75 Artillery
Tank Destroyer 1,125 Artillery
SP-Artillery 1,142.86 Artillery
SP Rocket Artillery 1,154.67 Artillery
Anti-air 1920 Artillery
Battlecruiser 972.97 Capital Ship
SH-Battleship 997.5 Capital Ship
Battleship 997.16 Capital Ship
Escort Carrier 984.38 Carrier
Carrier 1,102.94 Carrier
Industry 2,723.88 Construction
Naval base 2,727.27 Construction
Coastal Fort 2,727.27 Construction
Land Fort 2,727.27 Construction
Air base 2,769.23 Construction
Infrastructure 2807 Construction
Light Cruiser 1,050 Cruiser
Heavy Cruiser 1,050 Cruiser
Destroyer 1,000 Destroyer
Radar Station 720 Electrical
Strat Bomber 1,000 Heavy Aircraft
Transport plane 1,000 Heavy Aircraft
Infantry 1,106.75 Infantry
Mountain 1,335 Infantry
Paratrooper 1,500 Infantry
Engineer 1,540 Infantry
Marine 1,600 Infantry
Rocket Interceptor 1,428.57 Jet Engine
HQ 1,200 Land Doctrine
CAS 990 Light Air
Multi-role Fighter 1,071.43 Light Air
CAG 1,400 Light Air
Interceptor 840 Light Air
Naval Bomber 993.55 Medium Aircraft
TAC Bomber 1,005.71 Medium Aircraft
Garrison 501 Militia
Militia 665 Militia
Military Police 900 Militia
Motorised Infantry 934 Mobile Unit
Mechanized Infantry 1,000 Mobile Unit
AC 1,009.25 Mobile Unit
Cavalry 1,100 Mobile Unit
Nuclear(reactor) 9,000 Nuclear
Flying Bomb 600 Rocket
Flying Rocket 1,200 Rocket
Submarine 1080 Submarine
Nuclear sub 1,422.22 Submarine
Transport 900 Transport
Rocket 3,600 Rocket


At the end of every day time needed to research every tech with nonzero leadership dedicated to it is recalculated. This is then compared to the actual time spent researching the tech to determine whether the research is done. This means that if you gain a sudden decrease in research time (for example, if a large parallel construction suddenly finishes, giving you a boost in Practical Knowledge, or a new year begins, decreasing the penalty for researching ahead of the historical date), the research progress can suddenly jump forward. This is only done for active researches. If this sudden jump forward completes the project with extra days to spare, than these extra days are allocated to the next level of research (if not a one-time tech). The recalculations start at the top of the research queue and work to the bottom. If a tech completes, the Knowledge increase from it will be included in the recalculations below it. This can result in identical techs that complete on the same day having different completions dates for the next level of research (Knowledge increase from the tech higher up the queue reduces the required time for lower down tech resulting in spare days that are added to the lower tech's next research level).


Let's say you are researching Infantry Small Arms.

  • The difficulty level for this is 1, so the basic research time is 125 * 1.1 = 137.5 days.
  • Let's say you have a 4% research bonus from techs. This reduces the time to 137.5 * 0.96 = 132 days.
  • The research is 30% based on Infantry Theory, 60% based on Infantry Practical, and 10% based on Grand Battleplan Theory. Let's say you have a level 10 in the first two and a level 0 in the last. This shortens the time for the first two by 22.5% and lengthens the time for the last by 50%. The total multiplier to time is 0.775 * 0.9 + 1.5 * 0.1 = 0.8475. This reduces the research time to 132 * 0.8475 = 111.87 days.
  • Finally, let's say the year is 1940, but you're trying to research the 1942 tech. This increases the time by 100% for each year, or 200% total. The total research time is then 336 days. Better wait for it to complete on January 1 of next year!

The shortest possible research is a level 1 difficulty tech with full Knowledge level, and past historical date. If the above is correct, such a research would take 125 * 1.1 * 0.605 = 83.1875 days. Computing techs can reduce this further.

Knowledge Levels[edit]

You gain Theoretical Knowledge levels by researching techs, and Practical Knowledge levels by building and using buildings and units.

At the beginning of each month, all levels decrease by 2.5%. This can be reduced by certain ministers.

Knowledge levels are capped at 25.0.

Practical Knowledge decreases the IC and time needed to build a unit or building of that type. The maximum reduction is 22.4% IC and build time. This is multiplicative with Industrial Efficiency techs.


The effects given in the tooltips are the cumulative effect; that is, the effect of all upgrades up to that one combined. The tooltip days required (when moused over the Start button prior to commencing the research) and the dates listed in the research queue are calculated for that day's cumulative modifier only and do not account for expected changes due to Knowledge decay and/or Ahead of Historic Year modifier changes on 1 Jan of the next year (if research completion is projected to go into the next year).

Each upgrade seems to result in a 1% increase in unit IC cost and build time.