Hi everyone, today I thought we should do something different and take a look at how some concepts have changed over the Hearts of Iron game series. We'll be looking at supply, upgrades and reinforcement and such first.I didn't remember how it was here, and actually had to go buy myself a copy of the game online because I couldn't find any discsHOI1 has a pretty simple supply "system", a percentage of your total Industrial Capacity (IC) is diverted to supply production via a slider and goes into your supply stockpile. Units consume supply and if they run out they start losing organization etc. For a unit to be able to draw supply it needs to be able to trace a path to a friendly port or its capital. There was also a combat modifier penalizing you from fighting far away from your capital.Reinforcing had to be done manually (although you could do it for whole armies) by clicking on their strength to bring it back up.Upgrading divisions was a bit tricky compared to later games. You had to take them off map into the Force Pool, perform the upgrade by partially rebuilding it and then redeploy the unit on the map.These systems gave great control, but forced you to do a ton of micromanagement and keep track of a lot of things at the same time.Supply works a lot like HOI1, but introduces concepts like Supply Efficiency and Transport Capacity (TC). TC is a global value that gets automatically set as 150% of IC (could change by modifiers). Each division adds up to your total need of transport capacity depending on their supply consumption and if you go over it you start getting penalties. What directly effect a division is called Supply Efficiency which is an average of TC, local infrastructure and any bonuses from local HQ.Supply for divisions was now changed to be less micro intensive. You could prioritize armies and also give them special Offensive Supply when in a pinch. Doing so gave these units improved supply efficiency for a month at huge cost, but was good for your elites and critical offensives.Upgrading and reinforcement is now also less micro and done by diverting a percentage of your IC to it with a slider. You also had the option of producing attachments (like military police or anti air) to your divisions which could be deployed later.This basic system made for a lot less micro management, while only giving up some control (there is only really 2 prio levels since a division is prioritized or not), managing attachments was some micro, but it was a step in the right direction and gave great control. One of the major downsides of the system was that there was no real way of controlling Transport Capacity, so if you expand into in asia your front in europe will get same penalty when going over a global TC, but as an abstraction it worked pretty well.For HOI3 we wanted to expand on the supply system and make it more realistic. Supply and fuel are transported around the world in a province-by-province (and through naval transports) flow network.This system meant that there was a realistic delay built in when stuff changed and bottlenecks appeared and it's probably our most realistic system to date. The downside of this was that it was extremely hard to understand and follow (and also was very very bug prone). A problem a week ago could be causing your current frontline issues and because it was all a flow system with incremental changes being able to interpret how it was going wasn't exactly clear. What actions to poke the network with to improve things also was never really readily apparent for people without a lot of experience. We even added an "arcade mode" supply option that bypassed all the complexities and put it back to HOI1 level basically.Like HOI2 reinforcement and upgrades were now handled by diverting IC and upgrades.There is no way of prioritizing different armies or geographical areas, but you can tell units not to receive upgrades or reinforcement and in that way control where stuff is sent.HOI3 also expanded on divisions and basically made everything an attachment. This meant that you could reorganize brigades on the map by shuffling stuff around and do things similar to attachments in HOI2. The downside was that this was very micro intensive when you wanted to reorganize army templates as there was no way of doing it across more than one at a time.For HOI4 we changed the supply flow system to be instant and based around bottlenecks instead. The goal being that it should be easily apparent what is causing your frontline problems. We also moved to larger areas to get a better manage the complexity for calculations and display to player.When it comes to upgrades and reinforcement we made drastic changes in HOI4. They are now effectively the same things as you produce equipment rather than an abstract supply value to fill your divisions. We also added abilities to prioritize where supply went between theaters for better control, and even flagging division templates as elites, regular or reserves to manage their priority within theaters.Looking at the system I think gameplay went up on all accounts here. I think the system feels more realistic and immersive when looking at how you need to build exact equipment, but with fuel costs calculated into production of equipment rather than when using them (like on ships). There are some suspension of disbelief issues here we want to work on in the future.When it comes to managing upgrades of divisions compared to HOI3 we also made a big leap. It's now easy to do incremental changes to lots of divisions at once, either through editing their master division template, or changing a couple of selected divisions at once. Also upgraded equipment now slowly trickle into the divisions, upgrading them bit by bit in the field rather than all at once like in previous games.Team wise we are working on the expansion right now and should be able to start doing dev diaries on it soon, but let me know how this one felt, is it interesting to take a trip down memory lane?