Hello! It's time for another Hearts of Iron 4 Developer Diary, and this one is about Land Doctrines. For HoI4, we are leaning more towards the Doctrine paths you may remember from HoI2 than the mix-and-match of HoI3. We have 4 main mutually exclusive Doctrine paths which nations can research. Each path also has one or more mutually exclusive choices to further differentiate the doctrines and sub-doctrines. Because we are still pre-alpha, I can't really describe exactly what each tech in the tree does at the moment; this can and will change as we implement, test and iterate over them. I can describe the general idea behind each path and choice so hopefully you will understand what we are aiming for.This path focuses on mobile mechanized units and is the default German path. Armour and motorized/mechanized units will have the largest gains in this path. It also reduces the planning time needed before you can launch an attack. This path is somewhat frontloaded with early bonuses. The first branching in this tree allows you to choose between Mobile Infantry or Armour as your main focus. While Mobile Infantry isn't as effective in combat, it is cheaper and can be used in greater numbers, so it could be an alternate strategy for Germany, or be used by a less industrially powerful nation. The second split offers the choice between switching over to a defensive posture (maximizing Manpower gains) as Germany historically did, or continuing to develop offensive mobile doctrines. And yes, we know Blitzkrieg wasn't a formal doctrine, but the mishmash of innovations and new techniques that the Germans used is popularly known as such, so we roll with it.This is the American default path. This doctrine focuses on big, well-equipped, but expensive divisions and gains a bonus when fighting in areas with friendly air superiority. The first split offers the choice between adding more support units to each division, or focusing on independently deployed support brigades. The second split will let you pick between Airland battle (for increased cooperation with the air force for combat support) or Shock and Awe (which keeps the majority of your focus on ground-based firepower).This could be thought of as the traditional doctrine path, and is the default choice for Britain, France, Italy, and Japan. This doctrine path gives you larger planning bonuses and boosts Infantry and Artillery. It is a bit weak on the offence to begin with, but has some defensive bonuses. The split offers the choice between increased offensive potential and steadily improving all unit types with the Assault path, or focusing heavily on Infantry with the more frontloaded Infiltration path.The default doctrine for the USSR and China. It focuses on using large amounts of Manpower and offers increased morale and reinforce-speed. The early techs give some defensive bonuses and Infantry/Militia boosts. The first path decision here offers either continuing with the same methods with Mass Mobilisation (the mass use of Infantry and Militia) or adopting the innovative Soviet Deep Battle doctrine, which makes use of the modern tools of war and boosts the capability of Armour, artillery, and mobile units. You may notice from the image that the Mass Mobilisation path is shorter than the others. This is because it's more of a series of stopgap measures for nations in dire straits than a real doctrine, and we want to encourage nations to swap out of it when/if their situation improves."Swap out of it?" I hear you say. Yes, you can change your Doctrine path if you want. This will come at a cost. There will be a period of disorganisation for your army based on how far into your previous path you were and on the size of your army, so it's likely not something you want to do when things are going very poorly in the middle of a war. However, you do not necessarily start from scratch in your new Doctrine path: Several techs are shared between the paths, and if you switch to a path which includes a shared tech you have already researched you will start at that point in the new tree.Ok, that's about all for this DD, start trying to guess the tech names based on their icons!