The tooltips in the supply mapmode are invaluable, and hovering over different items shows different information:
- Unit: Unit supply draw, and where it’s coming from.
- Supply hub: Amount of supply requested of the hub, and highlights the railroad connection to the capital. Holding down the Shift key will show the range of the supply hub (at that time – range can change with weather).
- Port: Amount of supply requested of the hub, and shows paths to any ships that may be drawing Hub (but not State) supplies from the port. Holding down the Shift key will show the range of the supply hub (at that time – range can change with weather).
- Province: Total and available supply in a province. Holding down the CTRL key will also show a breakdown of where the hub supply is coming from.
Hub supply is the amount of supply provided by supply hubs or ports (which act as supply hubs, as well as ports). There are three elements to be mindful of when looking at hub supply:
- The total draw on the supply capacity of a supply hub.
- The range of a supply hub, and the amount of supply from the hub in a given province.
- Provinces received supply from all hubs in range.
In most situations, at time of writing, the most common supply issues are based on insufficient supply in a given province, rather than insufficient total hub supply capacity.
Total hub supply capacity
The total supply hub/port capacity is based on the connection between the hub/port and the capital, and for ports, the level of the port (both where the convoy departs, and where it arrives).
A level one railway connecting a hub to the capital provides 15 maximum supply from that hub, while a level one port connected to the capital by a railway also provides 15. However, a level one port connect to the capital by a convoy rather than by a rail connection has a base supply capacity of 20. Note that if the convoy route supplying the port is raided, the amount of supply provided will be reduced until the route has recovered its capacity.
For supply hubs, the base capacity increases for each additional level of rail connection to the capital, based on the smallest rail level at any point in that connection (so, for example, if there are three stretches of track, two at level 2, and one at level 1, the connection is considered to be a level 1 connection – to upgrade it to a level 2 connection, the level 1 stretch of track would need to be upgraded to level 2). Each level of rail connection increases the supply of a hub by 5, to a maximum of 35. if connected by river, the supply hub is considered to have a level 1 connection.
One exception to this is the capital supply hub, which has its capacity set at a base of 5 and then supplemented by the amount of civilian and military factories, and naval dockyards, in the nation. For ports, the base capacity for ports connected via convoys increases by 5 for each level of naval base, up to an effective maximum of 35 (or 65 if your capital has a port), as the amount of supply sent by convoy can never exceed the rail connection to the departure port.
Hub supply range
Supply hubs provide supply to each province based on a number of factors, the most important of which is the number of provinces between the province being supplied and the supply hub, with this being modified by the level of the rail connection to the supply hub from the capital, the level of infrastructure, terrain, and the weather.
Improving supply hub range
Outside of aerial supply, improvements to the level of supply in a province over the course of a game will almost entirely be due improvements in the amount of hub supply provided. The four means by which hub supply can be improved are by:
- Increasing the level of motorization of a hub or army.
- Increasing the level of the rail connection to the hub.
- Increasing the level of infrastructure in the area.
- Building a new supply hub.
Note that the first three methods (motorization, increase the rail connection level and increasing the level of infrastructure) all stack on top of each other - so a an un-motorized supply hub in a state with level 1 infrastructure and a level 1 rail connection would have the shortest possible supply range, while a fully motorized hub with level five infrastructure and a level 5 rail connection would have the longest possible range.
It's very important to bear in mind that hub supply falloff works increases significantly for every extra province distant from the hub, port or capital - so while it is possible to extend hub range, individual changes may be relatively small, and it will often take a substantial investment to increase range enough to push it out to the next province from the hub.
By default, each supply hub is set to “not motorized”, indicated by a horse. This can be improved by two different tiers of motorization, by clicking on the appropriate icon (see example below). Once a hub is motorized, one or two small trucks (depending on the level of motorization) will be visible as part of the supply hub icon (a green truck or trucks indicates that the hub has been directly motorized, while grey truck(s) indicates it has been motorized by a nearby army – more on that below). Note that trucks assigned to motorization of supply hubs, whether directly via hubs or by selection the motorization options for armies, do not consume fuel or manpower.
Depending on motorization level, each hub needs 0, 40, or 80 trucks (icon symbols: horse, one truck, two trucks).
The other way to achieve hub motorization, is to assign it at the army level. This automatically toggles the level of motorization set for the army on hubs that are in range of where the army is drawing supplies from. This has the advantage of reduced micromanagement of hub motorization levels, but it can lead to fluctuating demands for troops, as the number of hubs in range of the army changes over time. See the three screenshots and their captions below for an example of this in action.
Note that the full benefits of motorization will only be received if sufficient trucks are available. If more trucks have been assigned to support hubs than are available, then the benefits will be reduced, in proportion to the shortfall in trucks.
After motorization, increasing the level of the rail connection is the next most powerful and often (but it depends on how far the supply hub is from your capital by rail) the next quickest.
Each tile of railway costs 170 CIC, +130 CIC for each existing railway level (to a maximum of level 5), so it’s relatively quick and cheap to lay a level 1 railway down, but a long level 5 railway is a serious industrial undertaking. For example, as per the table below, the total CIC to build a railway from nothing up to level 5 is 2,150 CIC per province (170 + 300 + 430 + 560 + 690), adjusted for any construction bonuses and infrastructure effects on construction speed.
Actually building railways can be done in a number of ways:
- Selecting the supply hub, and then clicking the middle (top) of the three icons that appears. Each click of this will add another level of railway to each province on the rail connection to the capital (so, for example, three clicks on a hub connected by a level 2 railway will put construction orders in to upgrade it to the maximum level).
- Opening up the production interface, and selecting the “Railways” button, and then clicking on one of the white numbers in a black circle on a rail connection between two hubs – this will place construction orders to increase the rail level between the two hubs by one level. Each extra click will place construction orders to increase it by a further level.
Each additional level of rail will increase the size of the total amount of supply in the hub, which means the amount of supply flowing from the supply hub outwards is also increased. In some cases can mean provinces with no hub supply at all will receive some hub supply, although as noted above, the increasing size of "supply flow drop-off" the further from a supply hub means that extensions in range are likely to be limited.
Bear in mind that railways are also useful for strategic redeployment, and the higher the railway level, the faster troops will strategically redeploy.
If it looks like it’s not cost-effective, or possible, to get hub supply from existing hubs, it is also possible to build new supply hubs. On the coast, ports act as supply hubs, and are considerably cheaper (5,000 CIC for the first level of the naval base, with a further 1000 CIC added to the cost for each subsequent level). Inland, however, supply hubs need to be used, which require 20000 CIC (modified by any construction speed and infrastructure construction bonuses).
Both ports and supply hubs are constructed using the construction interface, shown in the screenshot below.
Both ports and supply hubs can be constructed in the territory of allies, and of subjects.
If it can trace a path using convoys, other ports, and railways back to the capital, a port will be supplied by sea without needing a rail connection.
A supply hub will also require a connection to the capital, traced via rail or river. Connection via a river is instant, and will be made if the new supply hub is connected via a river (bordering the province containing the supply hub) to either the capital, or another supply hub or port in a province bordering the same river.
To connect a new supply hub with a rail connection, open the construction interface and select the “railways” option, and then click on a province with a railway that is connected to the capital, and then click on the province with the new supply hub. The level of the railway constructed will be the same as that of the level of the railway in the province that it’s extending from, but this can be manually adjusted down or up levels (as long as the railway hasn’t been built yet) using either the construction list (the +/- buttons on the railway in the list) or on the supply map (left-click on small number (underneath the crossed hammers) on the railways under construction to increase the level, and right-click to decrease the level).
Railways can be built in controlled, allied or subject territory at any time, and do not need to wait for a supply hub to be completed (or even started).
Higher levels of infrastructure also allow supply from a hub to reach further, by reducing the drop-off in supply flow from the hub (to a maximum reduction in drop-off of 0.3 for level 5 infrastructure). Note that the level of infrastructure that matters is the level of infrastructure for state containing the province from which the supply is flowing. So, for example, if there are two states, a level five infrastructure state with a supply hub bordering a level one infrastructure state, the supply flowing from a province in the level five infrastructure state to a bordering province in the level one infrastructure state will flow as if it was level five infrastructure. However, supply flowing from a province in a level one infrastructure state to another bordering province in the same level one infrastructure state, will flow as if it was level one infrastructure.
As is the case for other ways to extend supply hub range, the increasing amount of supply drop-off as the distance from the hub (counted in provinces) increases means that any increases are likely to only be at the margins (ie, perhaps an increase of range of one province).
Be mindful that each level of infrastructure costs 6000 CIC – such that four levels of infrastructure in one state cost more than a new supply hub.
To run at full efficiency, supply networks need trains for rail connections, similar to the requirement of convoys for naval connections, with the amount of trains related to the amount of hub supply required from each hub. The train requirements for a hub can be seen in the tooltip for that hub.
Train requirements for the network as a whole can be found in the logistics tooltip, which can be brought up by hovering over the logistics icon at the top of the screen (it looks like a crate with a percentage next to it). If there are less trains than the network requires, there will be a reduction in hub supply available to divisions drawing it.
Trains are not subject to attrition, but they can be destroyed by air attack from enemy aircraft using logistical strike.
As well as the base model train, two other train models can be researched over the course of the game. One is an unarmoured “austerity” train – which does the same job as the base model, but at a cheaper price (50 MIC instead of 70). The other is an armoured train, more on which below.
Armoured trains are a special type of train that is more resistant to enemy Logistics Strike air missions. If you have armoured trains available in your inventory, they will automatically be used before other train types. Armoured trains have a significantly higher production cost of 105 MIC, so are much more expensive than the starting train and more than double the cost of the austerity train.
As a front advances into enemy territory, enemy-held rail lines and hubs may come under friendly control. While rail lines may or may not need repairing (rail can be damaged by strategic bombing, or by your opponent using scorched earth before they lose control of the state), they won’t be available for use right away in most situations. When capturing a railroad on territory that is not your core, the cooldown until the railroad can be used is 10 days, while it’s 5 if the territory is a core state, and there is no cooldown if the war is a civil war.
Rail conversion time
A newly-captured hub will only be functional once it is connected by “converted” railroads, and it won’t be connected until every province has had the required number of days under friendly control to convert. There is no conversion time, however, for supply hubs.
Both weather and terrain have an impact on the supply system - the tables in the weather and terrain pages on the wiki provide the figures for the various supply impacts for different terrain/weather states. Things to be mindful of when thinking about the impact of terrain and weather are:
- There are two weather effects:
- The Supply Factor reduces the flow of supplies from a supply hub (in-effect, reducing its range) acting as a percentage reduction on the supply flow into a province [to be confirmed]. These effects can stack if, for example, a region has a ground condition of deep snow and a weather condition of blizzard - deep winter conditions like this can substantially reduce the range of hub supply for the duration of those weather/ground conditions.
- The Supply Consumption Factor increases the supply use of a division. Both of these elements can be in play depending on the particular circumstances.
- There is one terrain effect:
- The Supply Flow Penalty Factor. This changes the supply fall-off in hub supply when moving away from the hub, and is added to other reductions in supply flow. This isn't a percentage figure, but rather a direct change (usually reduction, but it actually is an increase in urban areas) in the supply amount as it relates to the figures shown for hub supply in the province tooltips.
Unlike hub supply, state supply is a fixed amount of supply provided within a state, based on four things: victory points, infrastructure, population and something called ‘base supply’, which is a fixed amount of extra supply in a state. While state supply from population and infrastructure will be in every (non-impassable) state, a few states don’t have victory points, and many states have no base supply.
A state with a victory point in it will get 0.2 state supply from this, and then a further 0.05 supply for the total VP value of the victory points in the state (so, for example, a state with one 1-point VP, and one 5-point VP, would have 0.5 supply from VPs, made up of 0.2 base and 0.3 from 6 VPs in total in the state). See the table below for some examples:
Infrastructure provides 0.3 per level of infrastructure, as long as the infrastructure is undamaged (see the table below for infrastructure values) – if damaged, however, the amount of state supply provided by infrastructure is reduced until the damage is repaired.
Population adds supply on a diminishing scale from 0.01 supply per province in a state of 30.000 people, to 4.25 supply per province in a state with 23.6 M people. Converted to per 1 million people, the scale slides from 0.3 supply per million sparsely populated states to 0.18 supply per million in very densely populated states (e.g. Chinese states).
State supply is evenly distributed to all the units that are in the state (including air and naval units), before other sources of supply are used. Given this, it’s important to be mindful that while there might be enough state supply to support any units outside of hub range, those units will still have to share that state supply with units drawing supply from hubs or ports.
Understanding state supply is essential to understanding how the supply map mode “heat map” works – as unlike hub supply, the shading of each province on the heat map takes into account that total amount of state supply available for the whole state - but once that state supply is used elsewhere in the state, the available state supply for other provinces is reduced accordingly. Checking an area to see whether the heatmap shading is due to mostly hub or state supply will provide a clearer indication of the effective supply in the province if more forces are moved into the state in other provinces. Please see the example provided by the two screenshots below for a bit more detail.
If control of a state is split between two countries at war with each other, the amount of state supply will be split in two. Hub, population and infrastructure elements will be allocated based on the proportion of the state’s provinces owned by each side, while state supply from victory points is provided to whoever owns the provinces containing those victory points.
The final of the three pillars of the supply system is aerial supply. Aerial supply is provided by transport aircraft flying “Air Supply” missions. Like state supply, the total amount of supply provided via this is available in any province in the air zone in which the air supply mission is flown (regardless of whether it is in range of the transport aircraft or not). However, unlike state supply, air supply is drawn last, so units only draw on air supply if they cannot meet their full supply requirements from state and hub supply.
As is the case for any air mission, the mission efficiency will reduce the amount of supplies that can be provided, and efficiency can be impacted by a range of elements, including weather, the supply status of the squadron performing the mission, and the relationship between the size of the air zone and the range of the squadron. At 100% mission efficiency each fully supplied transport plane flying in good weather is capable of providing 0.2 supply per plane.
The supply requirements for an air wing are determined by the amount of supply they are able to provide via their mission efficiency – so all else being equal, a wing of transport aircraft that can cover a greater proportion of the air zone will provide more air supply than the same sized wing using a different airfield that gives it less coverage. Transport air wings flying air supply missions can only use state and hub supply, and can’t draw themselves on air supply.
The amount of supply a division requires for full supply is based on a range of elements, including the line battalions, the support battalions (logistics battalions reduce overall supply use), weather and the capabilities of their commanders.
If a division is below full supply, a faded or bright red crate icon will appear on its on-map icon, and on its icon in the list of divisions in the army. To get a precise look at a division’s supply status, hover over the icon in the army division list to bring up the tooltip. A division’s supply will move towards the amount that can be supported in the province, whether that’s up or down. So, for example, if a division moves from a province where it is 100% supplied, to one where it is 50% supplied, for the first hour in that new province it will still have 100% supply, and then the division’s supply state will go down as its stored supply runs down to 50%.
There are significant penalties for being out of supply to a range of unit characteristics. Note that there can be a delay between a low supply state being reached and the full penalty kicking in. Unit characteristics impacted by low supply, with the impact increasing as the supply state deteriorates, are:
- Max organisation
- Org regain speed
- Attack (with a higher max penalty for units defending (-50%) than units attacking (-20%))
- Breakthrough (for units attacking)
- Defence (for units defending)
- Attrition - if a unit’s level of supply drops to 35% or less, it will begin to take supply-based attrition, increasing the amount of equipment the unit uses by increasing amounts the further supply drops.
Being in a low supply state also has an impact on how quickly manpower reinforcements arrive. As long as a division has a connection to the capital via a continuous path through friendly provinces, ports and/or convoys, manpower reinforcements will arrive - although at very low supply levels they can take a long time. Note, however, that the speed of equipment resupply is not affected by a division’s supply state (but if a division has low supply they will experience constant attrition for as long as this is the case, which may prevent a division from reaching its full equipment levels).
If a division is cut off from the capital, even if it is in full supply due to occupying a victory point or another source of state supply, or due to air supply, it will not receive manpower or equipment reinforcements.
Note that fuel works a bit differently to manpower or equipment. Like manpower and equipment, if a unit is cut-off from their capital, it won’t be replenished. Like manpower, the rate of fuel resupply slows if a unit is not fully supplied. However, unlike manpower, fuel supply stops entirely once the supply state is sufficiently poor. Air supply does not impact fuel supply, so even if a unit can trace a line of provinces to its capital and is fully air supplied, if it doesn’t have enough state or hub supply it may not receive fuel resupply.
Stored supply/supply grace
Supply grace and stored supply refer to the same thing, which is the amount of supply greater than 100% that will be stored by a division if it is in a fully supplied province. The amount of stored supply for a division can be seen towards the bottom of the tooltip that comes up when hovering over a division’s name in the Army UI element, as per the example below.
The base amount of stored supply that a division can accumulate is 150%. The rate at which it drops varies, but it should enable a division to operate for 2-3 days at full supply efficiency even if the province it is in is not fully supplied, before the stored supply drops below 100%.
For special forces divisions some technologies can increase the length of supply grace. This can be further extended for Marine divisions if they are lead by a general with the “Amphibious”. The extra supply grace provided is described in terms of hours, but this is only broadly indicative, as the rate of reduction in stored supply can vary depending on the situation the division finds itself in.
An air unit’s supply is based on the level of supply in the province containing the airbase. If an air unit is flying a mission and is not at 100% supply, it will have a malus on efficiency due to its reduced supply level. It is important to bear in mind that if supply falls below a threshold, the air unit will also not receive enough fuel, reducing mission efficiency even further.
For naval units, being less than fully supplied impacts directly on spotting efficiency and repair speed, but it also reduces the rate of fuel received, which depending on the fuel situation can have an impact on their efficiency in combat as well. It is worth bearing in mind that naval units have access to the full amount of potential supply from the hub they're drawing supply from (rather than being limited by what the province can support as well, as per land and air units), so it is far, far less common for naval units to be undersupplied than it is for land or air units.
By default, you can draw supply from your allies’ supply hubs, and your allies can draw supply from your supply hubs. Note, however, that if you’re fighting on allied territory, you can’t use the state supply system. Allied divisions share hub supply with divisions of the host country, but the host country divisions will probably be a bit better supplied as they’ll be able to access whatever state supply is available as well.
While the AI won’t do this, if you want allies not to be involved on a particular front, it’s possible to toggle off supply for allies on a hub-by-hub basis. To toggle supply for allies off (or back on) for a particular hub, click on the hub, and then select the blue flag to the left and above the supply hub symbol (see examples below).