Every land army needs a constant supply of food, ammunition, and shelter. These necessities are referred to collectively as supply. In the EU2 timeframe, most of the food an army ate, and often much of its shelter, was simply commandeered from the local area it was in.
Naval units also need supply and suffer attrition for lack of it. But they do not live off the land in the same way that land units do, and so the effect of naval supply is much simpler. See the article on naval attrition. Unmodified mention of supply in the EU2 wiki means land supply, not naval supply.
For information on the concept of supply and demand of trade goods, see the article on goods.
Effect of Supply
There is only one effect of supply, but it is a hugely important one: in computing land attrition. Armies that don't maintain good supplies (or who venture into terrible places such as African swamps or Russia in the winter), tend to melt away from disease, desertion, and death.
Sources of Supply
Although the main source of supply is the province an army is in, there are several other factors than can affect supply.
The supply for each army in a province is computed starting with the province's base tax value. It can be multiplied by up to a factor of 5, based on the relationship of the army's country with the owner and/controller of the province. If more than one apply, the best multiplier is used:
- 1x if the province is unowned.
- 2x if the province is owned, even if just a trading post.
- 3x if the army's country controls the province.
- 4x if the owner of the province has given military access to the army's country.
- 5x if the army's country is the owner of the province.
- 5x if the owner is a war ally (in the same war coalition) as the army's country.
This supply level can be doubled, if the province is a blockaded enemy port province.
For provinces that are owned by the army's country, or a war ally, or a country giving the army's country military access (regardless of who controls them), the supply is raised more by the following:
- 10*F, where F is the fortification level of the settlement.
- +10, if the city has a conscription center.
The resulting supply level is referred to as the "displayed supply level" (DSL), because it is the number for supply that you can see on the province screen when you select a province. You can also see it by selecting an army, then hovering over the attrition display to get a tooltip; the DSL is shown on the tooltip as "Province Supply".
The actual supply limit is not shown in the game, so it is important to know how it is computed. Starting with the displayed supply limit, we add a bit of extra supply for the leader, then reduce the supply for tropical provinces, and reduce it further if the province is in winter.
Every leader adds a small amount of supply to the army he is commanding. For default leaders and generals, 2x their manuever number is added to the supply level. For conquistadors, 4x their manuever number is added. Note that leaders supply only their own army, not any other armies present in the same province.
Next we subtract supply for bad climate or winter. These are:
- -5: tropical climate in province
- -10: winter in province that is owned by the army's country.
- -25: winter in province that is not owned by the army's country.
The supply "tail" of EU2 armies was not huge, especially at lower tech levels, and they would live off the land. However, supply lines are computed by EU2 and do have an effect, in the computation of maximum attrition. Every land army is either "in supply", or "out of supply", according to whether it can trace a line of covered provinces to a province that is controlled by its own country or a war ally.
Out of supply occurs in all provinces except for provinces:
- controlled by you. (The displayed supply limit is shown in green.)
- controlled by a country in a war coalition with you. (Green DSL is shown.)
- covered by you, and an unbroken chain of covered provinces can be traced back to a province controlled by you or a coalition partner. (DSL is shown in yellow.)
- adjacent to any of the preceding. (DSL is shown in yellow.)
Thus, your supply lines can reach arbitrarily far into enemy territory, but you must at least cover every province in the chain, back to some province controlled by you or a war ally.
If a province is out of supply for your country, you'll see the DSL number in red.