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HOI4 Dev Diary - Traiiiiins

Greetings, and welcome back for our last look at the supply system that ships with the Barbarossa update. As you all know, I’m British, and in Britain the trains never run on time - I couldn’t possibly break with this tradition, hence a completely intentional 10 minute delay on today’s diary.

There’ve been a couple of changes since we last looked at this, so you may find I’ll be reiterating a few aspects that we’ve already covered in previous diaries, albeit in some cases with a new twist.

Trains

As indicated in a previous diary, the logistics network that supplies your troops relies on the large-scale relocation of supply using trucks and trains.

Whereas trucks serve as an optional last-mile carrier for military supplies, trains make up the backbone of any logistics network that supplies an army which exceeds the local state supply available in its location.

The domestic production of trains is something that is unlocked via the technology tree. Many countries will start with the initial (civilian) train technology readily unlocked, however, there are several more options available to you as time progresses (more on this below!).

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Your overall train need for the logistics network is derived from the overall supply usage of the nodes supplying your troops, and the distance factor that supply has to travel in order to reach them. In essence, the more troops you have drawing supply, the more trains you will need to keep supply running.

Needless to say, if fewer trains are provided than are required, supply output at point of demand will incur penalties proportional to the magnitude of the shortfall.

In one of our previous diaries, we alluded to a number of interactions that could be performed on supply nodes - one of these was a train priority setting. It transpired that this did not fit well with the underlying simulation, and we’ve removed this setting from nodes.

Logistics Strike

Of course, a freight-train loaded with supply makes a juicy target for the enemy. In NSB, CAS and bombers are able to perform the new logistics strike mission, which can put a severe strain on an enemy’s ability to supply their network - actively destroying trains and trucks, as well as damaging railways in the target area.

The strategic bombing air mission will also target rail and supply infrastructure, however the logistics strike mission is a much more effective way of neutralizing an enemy’s fighting capabilities while retaining important industrial infrastructure if you intend to occupy an area for any period of time.


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Train Variants

As mentioned above, trains will be a researchable technology with several variants. Trains, unlike regular units, are not controllable - their movement and behaviour is entirely simulated based on the needs of your logistics flow. This said, there are several important statistical aspects to them.

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To begin with, most of your network is likely to be populated by civilian trains. You can construct more of these by co-opting military factories. Further on in your campaign, you can unlock a variant of the civilian train with a significantly reduced construction cost.

To combat the strategic mission mentioned above, there is one (or..is it more?) further item in your toolbox for owners of the NSB expansion. Armored trains, while coming with a higher price tag, are much more resistant to destruction from air missions, and can act as an effective deterrent against logistics disruption.

Train enthusiasts (we have none of those here, right?) will note that the trains displayed above belong to the soviet union - there is indeed unique art as well as 3d models for several other major nations.

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A highly camouflaged train in action.

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Displayed trains are based on your stockpiled train equipment. This is the german armoured locomotive!

That’s all from me for today - I’ll hand over here to @YaBoy_Bobby to go over some of the details on supply distribution at a hub level:

Hub to Province Supply Distribution

We have talked about how trains and rails feed the supply hubs, but not so much about how hubs feed divisions in the field. As hubs are fed from the capital province by a rail network, divisions are fed by hubs over land.

Every Hub has an overland range that gives it a collection of provinces that it touches. This range is constant, but the cost of moving over each province is impacted by things like weather, terrain, rivers, and infrastructure. Motorization decreases the penalty for crossing each province, thus increasing the number of provinces a hub will touch and potentially creating greater hub density and thus greater overall supply in an area.

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As has been alluded to with the phrase “hub density,” a province may be touched by multiple hubs. When multiple hubs touch a province, a ratio is created to determine what percentage of the supply requested each hub is responsible for. Every hub that touches a province lessens the supply burden of other hubs also touching the province.

In the final step, Divisions draw supply from hubs, depending upon the relationship between their current province and the hubs that touch that province. When a hub does not have enough supply to meet demands, the lack of supply is distributed evenly across all divisions currently drawing from the hub.

In older DDs we talked about a penalty to the amount of supply delivered to a province based upon weather, terrain, and distance. Over the summer we decided to remove this penalty as we found it compounded in a hard to predict way that created bad supply and sometimes penalized having more hubs touching a province in a way that we did not like.
 
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I do remember they changed the gauges at the end of WWII, and that there exist rails that cover multiple gauges. Otherwise, they can just switch trains at a depot.
Incredibly hard to do as you need to have enough available ready to use locomotives in the area. If the enemy has a different rail gauge than you have, tough luck, as you should be forced to use their often bombed out or sabotaged railways, and you would have been forced to use their own locomotives, but you cannot, because they either took it with them or destroyed them on their way out. Or you would have to painstakingly adjust the enemy railways, costing you valuable time, material and manpower that you do not have.

As what the Axis forces experienced in the Eastern Front.
 
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Every Hub has an overland range that gives it a collection of provinces that it touches. This range is constant, but the cost of moving over each province is impacted by things like weather, terrain, rivers, and infrastructure. Motorization decreases the penalty for crossing each province, thus increasing the number of provinces a hub will touch and potentially creating greater hub density and thus greater overall supply in an area.
and
In older DDs we talked about a penalty to the amount of supply delivered to a province based upon weather, terrain, and distance. Over the summer we decided to remove this penalty as we found it compounded in a hard to predict way that created bad supply and sometimes penalized having more hubs touching a province in a way that we did not like.
This sort of confused me. Does this mean supply will be affected by weather and terrain but only insofar as it'll affect the range in which supply will be delivered? (So all supply within a ranger whether it's 1 tile away or 3 tiles (provided no supply posts overlap either) will have the same amount of supply?
 
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Whew sorry I dont have time to go through 11 pages of comments but

How will the new supply mechanics affect countries invading over water? Will there be a beginning with horse-drawn or motorized or human-powered logistics before transitioning to railways if they aren't there or heavily damaged? Will trains be locked by geographic area or rail gauge? Will occupying forces be able to use "captured" trains?
 
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Very promising, it's getting better and better, but yet I feel like some of the stuff is still way too unfinished or not really planned out.
Will you be able to consturct the hubs? Why can't you build warehouses to increase the range of a hub or would be the infrastructure?

What if you only need supply to flow in one specific direction?
Camels and Horses are often better suited for deserts than trucks, is that gonna be simulated.
If we have supply strike that means our hubs need protection. Can we build the AA for that?
Are Tactical Bombers gonna be better at striking hubs than CAS and shouldn't heavy fighter be able to do so too?

Do transport planes for supply still need a lot of command power or is there a plan for that to be decreased?
 
I'm really looking forward to the update and NSB DLC. I'm new to Paradox, I only started PC gaming when CK3 dropped. But I've become such a fan, that I've went back and purchased every single game. Except HOI 2 and 1. I'm a big fan of the way supply will be more historically accurate in the coming update! I'm hoping to see a much greater game soon!
 
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1. Can I capture enemy train? Both during fighting and capitualting a country?

2. Can I completly destroy an enemy supply hub with logistical strike? Can I destroy mulberry harber as well?
 
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I like those changes: trucks and trains - less unit spam. Only problem i see: you can kill logistic using planes - you can win war by using only planes. I dont wanna go back to meta with 90% mils on fighters. I hope those trains will be more plane resistain than ships :p.
 
In the final step, Divisions draw supply from hubs, depending upon the relationship between their current province and the hubs that touch that province. When a hub does not have enough supply to meet demands, the lack of supply is distributed evenly across all divisions currently drawing from the hub.

@Arheo Do elite divisions get priority in receiving supply in this circumstance, or do they get the same supply as any other division in the area? If I have tanks and some fodder divisions to cover the frontline in the supply area, I would much prefer to have an option to give supply to my tanks first, for instance.


No. Countries starts with some trains, depending on its size. The amount of trains needed obviously scales with the amount of units you field and the size of the front you fight on. I recently did an Australia playthrough and if you plan ahead it is totally manageable. It becomes a problem if you ignore it or someone bombs them and you suddenly need to produce vast quantities of trains in a short timeframe

*cough stuck in Siberia cough*

Its a big issue if you are stuck without trains in lower infra areas of the world (Middle east, Parts of Russia, China (most of Asia in fact), South America etc)

@CraniumMuppet This may be a stupid question, but how are you supposed to transport your trains from Australia to, say, South America? Was transporting trains via sea a thing? Is it possible to sink trains being transported in a convoy? I mean you are not flying the things to the frontline are you?
 
Let's talk about modding for a moment. When creating a custom rail network, do we merely open the StateFileID and write down which provinces contain train tracks, and they connect to each other automatically; or is there a separate fail where we designate a line (Berlin-Dresden for example) and write down the provinces with train tracks?
 
Incredibly hard to do as you need to have enough available ready to use locomotives in the area. If the enemy has a different rail gauge than you have, tough luck, as you should be forced to use their often bombed out or sabotaged railways, and you would have been forced to use their own locomotives, but you cannot, because they either took it with them or destroyed them on their way out. Or you would have to painstakingly adjust the enemy railways, costing you valuable time, material and manpower that you do not have.

As what the Axis forces experienced in the Eastern Front.
Good point, good point. Actually, you've got me wondering now: do you think Germany had any plans for a train that changed gauges without stopping? It honestly wouldn't be the weirdest rail-related or Germany-related design I've ever seen.
 
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@CraniumMuppet This may be a stupid question, but how are you supposed to transport your trains from Australia to, say, South America? Was transporting trains via sea a thing? Is it possible to sink trains being transported in a convoy? I mean you are not flying the things to the frontline are you?
Convoys transport supplies across the sea. They land at a port and then your trains takes them by rail
 
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@CraniumMuppet This may be a stupid question, but how are you supposed to transport your trains from Australia to, say, South America? Was transporting trains via sea a thing? Is it possible to sink trains being transported in a convoy? I mean you are not flying the things to the frontline are you?
Yes they Literally shipped trains from the USA to the UK and then to France for D-Day
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I'm a little surprised that World War Wednesday streams haven't restarted yet.

It definitely doesn't bode well for a timely release date, but if a bit of a delay means more polish and hopefully a more fleshed out and refined White Guard civil war and focus tree, it'll be worth it.

The new logistics system is looking better and better, and this new logistical strike mission sounds like it could add a new layer of strategy and perhaps give Tactical Bombers more of a niche if logistical bombing is its own stat.

It will also be hard to balance. If logistic strikes are too effective, then you can end up with a situation where an army is more or less starved out on its own turf. The last last year and a half, two years of the war, the Germans had lost control of the skies completely and were at the mercy of allied bombers, but weren't starved out so easily.

I could also see some more choices being helpful here. What if you could set trains to run only at night, reducing the supplies that get through but reducing vulnerability to logistic strikes by some huge percentage?

I also worry that we could end up with cheese like the Western Allies running missions in Western France to take out a few German trains supplying coastal garrisons and end up starving the Germans out on the Eastern Front. It'd be like if for naval convoy interdiction if you weren't allowed to tell your convoys not to go somewhere. Imagine if you weren't able to say, block convoys going to Malta as Britain and the Axis deliberately doesn't invade it just so they can keep killing convoys? It seems like this kind of cheese will be possible with the new system of ground logistics and trains.
 
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Very nice DLC.
Whats about a new additional feature:)?

We can now build Trains and more.
But i can not destroy it.
It will be nice when i can destroy the Railways/Bridges/Buildings with my own units.

The Germans and and the Sovjets used the tactic of Scorched Earth (German: "verbrannte Erde").

Idea for HoI4?
 
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Is there any intention to add the movement of Nuclear Bombs to arm strat bombers at air bases via trains? As this might be a way of stopping nuke spam in late game.
 
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