This article describes the logistics system in HoI3, focusing on the mechanics of supply depots, the supply network, and supply throughput. For strategic advice on logistics, visit the Logistics strategy article. Note that the Semper Fi expansion adds a new, optional game mode called "Arcade" where the entire supply system is circumvented. In this game mode, supplies are simply drawn directly from a national stockpile.
Supply depots (aka "supply sources" or "supply centers"), are a physical location on the map where a nation's supplies are automatically stored. All supplies created for the national stockpile are either stored in supply depots, in transit in the supply network, or are actively consumed by units. In this sense, the supply counter in the main screen toolbar is only an abstract aggregate: there is no single national stockpile.
- Every country has a primary supply source located in its capital.
- The overseas supply source for any territory not connected to a nation's main land is a port.
- Supplies are automatically distributed from the supply source to all core national provinces with IC.
Apart from supply sources, any province that has received more supplies than the units in that province used will temporarily store these supplies. Thus, these supplies can be captured if the province is captured. After a short period of time, any provinces with surplus supplies (other than a supply depot) will send them back to a supply depot along the supply network. There is no throughput cap on supplies heading back to the center, and no supply tax.
The game has one principle supply network method used for transporting supplies on land and overseas:
- All units draw supply by requesting it from the province they are located in.
- If a province cannot supply a local unit, it will request supply from an adjacent province:
- The first province asked will be the one located closest to the supply source.
- Every other adjacent province will be asked if a previously asked province cannot provide supply.
- If one adjacent province cannot meet the total supply need, multiple adjacent provinces may be used.
- Each province between the requestor and a supply source will carry the request for supplies forward, aggregating other supply requests as appropriate.
- Supply moves one province per day.
There are three ways for a player to manually manipulate the supply network:
- Transport planes: While transport planes are very expensive, carry limited supplies, and generally require air superiority, they can surgically augment areas with supply problems.
- Convoys: AI control of convoy creation and destruction can be turned off, allowing a player to manually create convoys.
- Supply re-route: Starting in Semper Fi, it is possible to create sea convoys to improve the supply flow to areas already connected via land to the supply depot (Lenningrad and Vladivostock: in addition to a land connection, can also have a sea connection). This can happen so long as the provinces involved are separated by at least 10 provinces.
The supply map effectively shows that the supply network is not a static network, but instead a constantly changing network based on unit needs. Thus, this map mode is a snap shot in time, not a comprehensive view of what your supply network might be capable of in different circumstances.
- Green shows it is receiving all of its requested supplies and every unit is in supply.
- Blue shows a supply surplus.
- Black shows zero supply, zero requests
- Brown shows province has a supply deficit: demand is higher than throughput. Effected by infrastructure level, terrain, or tech level.
- Red hatching shows limitation being imposed on the infrastructure.
- Red shows demand draw is greater than required, province may or may not have supply, throughput is zero.
For more details, view this post by potski on the HOI3 forums explaining the supply map and many intricacies and implications of supply draw.
Allies & Puppets
When units are in an allied nation, supplies will be drawn from the allied supply network. Meanwhile, an automatic and invisible trade route will be created between the two nations, where the exact amount of supplies and fuel will be sent from the nation with its troops abroad to the allied nation hosting those troops. As a result of this system, supplies, fuel, or resources cannot be transferred through a puppet or ally. For example: consider that Japan is fighting near Beijing and has existing supply through north-eastern ports in China. Japan will not get supplied through Manchuoko by the Korean supply network. Note also that the "transit rights" agreement is only applicable to unit movement and stationing, and does not have a bearing on supplies.
There are several factors that limit the distribution of supplies:
- Infrastructure: The supply throughput a province can funnel depends on its infrastructure (see below for details).
- Supply Tax: Moving supplies costs a base tax of 0.1 supplies (decreased by Supply Transportation techs) per province moved through.
- Port Size: For overseas supply sources, the size of the port (each level equals 4 supplies) limits the amount of supplies that can be convoyed.
- Air Base Size: Each level can support 4 supply units. Thus, a level 10 airbase can supply 40 air wings maximum.
- Partisan Activity: Partisans will disrupt your supply in any province with partisan activity, decreasing your supply throughput.
Supply Throughput can be improved through the following methods:
- Supply Transportation research reduces the supply tax per province.
- Laws can also affect supply throughput. Mixed Industry gives 5% bonus to throughput while Heavy Industry gives a 10% bonus to throughput.
- Less draconian occupation policies will decrease partisan activity and improve supply throughput in occupied territory.
- The Army Group HQ will improve logistics by 5% based on each skill level of its commander.
- Building new infrastructure will increase the throughput of that province.
- Building IC in a core province without IC will create a new supply source and possibly improve nearby supply distribution.
Effect of Infrastructure
The exact workings of the supply system are not fully known. Maximum throughput has been determined to be:
4 * (1 + modifiers) * OAC * infra²
- infra is a number between 1 and 10. The infrastructure percentage gets divided by 10 and rounded down to a whole number. So a province with 29.9% infrastructure and one with 20% both have an infra of 2.
- OAC is 2 if the province is Owned And Controlled by the same nation, otherwise 1.
- modifiers are given by ministers, technology and strategic effects.
This was tested in a "linear" situation, that is a non-branching path of provinces. Maybe this limit is averaged over 2 days. It is unknown what happens when paths branch and merge.
Due to the quadratic dependence, it is more efficient to build up a single supply path to level 10 infrastructure than to have several paths at lower level, though there is also the strategic weakness of being vulnerable with only one supply path.
Ports and Supply Convoys
Wherever possible, a supply route will be created over land instead of a sea route. This is true even when the land route may be much longer than a sea route (e.g. when wrapping around the Mediterranean Sea, for example). In Semper Fi, it is possible to avoid this problem and manually route supplies via the sea.
Ports: Overseas supply functions with an origin port and a receiving port. The most efficient origin port is a national core province with IC, thus acting as a supply depot, with high infrastructure and port level. While an origin port can theoretically send an unlimited number of convoys, a receiving port overseas can only receive one supply convoy and send out one resource convoy. Manually trying to game the system and make two supply convoys by ticking the appropriate boxes does not work. The supplies an overseas port can receive is limited by port level, with 4 supplies per day per port level. A level 10 port can thus receive no more than 40 supplies per day which can, for example, support about 15 infantry divisions with artillery. Therefore, large overseas forces require more ports in areas linked to your port ( = more possible supply convoys) or supply them by air.
Supply Convoys: Supply convoys use a number of transports equal to the length of the route (measured in terms of sea provinces) in order to operate at maximum capacity for the receiving port (determined by port level, as described above). Starting in Semper Fi, if units overseas need more supplies than the local supply depot can provide, additional supply convoys can be sent to other overseas ports. This will not create new supply depots overseas, but these will overcome the bottleneck introduced by the port size of the supply depot. Thus, all additional ports opened will funnel supplies to the local supply depot, which will then disperse supplies as needed.
Lack of Supplies
Every unit has a 30 days reserve of supplies and fuel. If there are not enough supplies available, it will begin consuming that reserve and you will notice the out-of-supply-icon warning you that this unit is beginning to draw on its reserve. The unit immediately suffers from a reduced combat effectiveness, with a penalty induced relative to your reserve level. For example, with 20 days supply left (66%), the unit will suffer 50%*(1-(66/100)) = 16.7% combat penalty.
If the 30-day-reserve is completeley exhausted, a unit will no longer be able to move. The penalties then are:
- -50% combat modifier
- Can not move
- out of fuel = slower movement (only applies if you have still have supplies)
- you do not get reinforcements or upgrades
Units out of supply will not reinforce, regain organization or upgrade, hence attrition will occur resulting in a strength loss. Combined with tactical bombing, this can reduce the strength of any fortified province to be enable an assault. Note that different units draw varying levels of supplies. Infantry will always draw less supplies than motorized divisions, for example. When strategically redeploying units, supply draw is doubled.
Research that effects supply
- Large Front: reduces supply consumption -0.1
- Guerrilla Warfare: reduces supply consumption -0.1
- Airborne Warfare Equipment: reduces supply consumption -0.1 (paratroopers only)
- Supply Transportation: each level reduces transfer cost by .01
- Supply Organization: each level increases throughput by .05
- Port Efficiency: Base supply per port level is increased up to 25% (e.g. each level base can support 5 supply)
Due to issues some players have with constraints in the supply system, simple modifications can be made to the game's text file to change the way supply is handled. In the "Defines.Lua" file in the Common folder, the following variables are key:
- SUPPLY_TAX = 0.1 [the additional cost per "node"]
- MUDDYNESSSUPPLYTAXMODIFIER = 0.25 [additive to Supply tax for provinces in muddy conditions]
- OWNED_AND_CONTROLLED_THROUGHPUT_CAP_BONUS = 2 [Maximum bonus possible for throughput in a nation's controlled provinces]
- INFRA_THROUGHPUT_IMPACT = 4, [Number of supplies that can be moved per infrastructure level]
- SUPPLYPOOL_DAYS = 30 [Number of days a unit has local supply stocks without needing the supply system]