Hi — I’m Jack, the newest Game Designer on the Hearts of Iron IV team. I’m thrilled to present a substantial overhaul of the Doctrines system.
This subsystem has remained largely the same since launch, so when I was asked to redesign and expand it I dived straight in. The redesign is the product of many conversations and iterations — special thanks to Zwirbaum (Tomasz) for his patient feedback and for tempering some rather ambitious balance ideas — and to our community of beta testers who helped sharpen the details.
Note: the feature is still a work in progress. Some elements are likely to change before release as we continue to incorporate feedback and polish the system.
The goal of the doctrine rework is to make progression more deliberate and gameplay-driven. Rather than selecting a single static tree and instantly reaping all benefits, you’ll develop doctrine strengths organically by fielding, training, and deploying units. In short: play with your formations on the map — use your troops in combat — and those actions will meaningfully improve how they perform. We also want to encourage experimentation with division designs and strategic approaches, giving players room to explore different combinations and tactics.
Here’s the new doctrine screen:
Grand Doctrines & Subdoctrines
The most visible change for returning players is the split between Grand Doctrines and subdoctrines. A Grand Doctrine represents the broad strategic direction you want your armed forces to follow, while subdoctrines provide targeted improvements for specific unit types or roles. Subdoctrines are the more granular, customizable component — they determine which units receive focused enhancements.
If your nation doesn’t begin with a Grand Doctrine pre-assigned, the first step is to choose one.
Once you select a Grand Doctrine you’ll see the Tracks available to customize your doctrinal priorities.
Category Tracks
Subdoctrines are chosen by category, or Tracks. For Land Doctrines the typical tracks are: Infantry, Combat Support & Artillery, Armor, and Operations. You may assign one subdoctrine per track (modders: the system accepts an arbitrary number of tracks). Selecting a Grand Doctrine and its subdoctrines consumes Army XP, and some benefits are granted immediately. However, not every bonus is instant — many unlock progressively as you gain experience using the relevant units.
Mastery & Mastery Levels
Alongside Army XP we’re introducing Doctrine Mastery (or simply Mastery). Mastery represents hands-on experience earned by deploying and using units tied to a specific track. Mastery is tracked per track, so to increase mastery you need to operate the unit types associated with your chosen subdoctrines.
Combat deployment is the primary source of mastery, but you can also gain incremental mastery through unit training, military attachés, faction sharing, and certain national focuses or decisions. By default each track maps to a set of mastery-generating unit types; subdoctrines can override those associations where appropriate.
Mastery accrual is based on deployed manpower in combat and uses diminishing returns beyond certain thresholds. This design helps prevent minor nations with small forces from falling completely behind while still allowing major powers with large armies to progress more quickly. Each mastery level requires a set number of mastery points, and reaching higher mastery levels unlocks stronger bonuses for the units in that track.
Mastery Banking
Mastery can be banked even if you haven’t yet invested in a particular subdoctrine (within limits), or if you’ve fully mastered a subdoctrine and continue using those units. This ensures you won’t entirely lose out on experience simply because you used troops before choosing or changing a subdoctrine.
Milestones
Completing a track grants a Milestone — a reward that benefits your Grand Doctrine directly. Some milestone bonuses may also appear within subdoctrines, which allows for interesting synergies. For example, Mobile Warfare’s milestone can include improvements tied to planning speed. Bear in mind: replacing a completed subdoctrine removes its milestone, and changing Grand Doctrines late in the game can be costly because it wipes progress on existing subdoctrines.
Below is a fully populated Land Doctrine screen (Air and Naval doctrine trees follow the same principles). Here the four tracks each have an assigned subdoctrine progressing toward their final rewards, and the Grand Doctrine has an unlocked milestone.
Officer Corps Window
The Officer Corps interface and doctrine icons have been updated to reflect progression: doctrine icons subtly change as you unlock reward tiers, and you’ll receive discreet event ticks when new doctrine rewards become available.
Smaller Updates: Army Spirits
Army spirits are being adjusted to tie into subdoctrine completion in a similar way to milestones. Unlocking a subdoctrine can bestow an army spirit, and once unlocked that spirit behaves like a tradition — it can persist even if you later switch subdoctrines. These spirits also provide additional sinks for army/navy/air XP, which helps balance the new doctrine mechanics. As an illustration: completing a “Mobile Infantry” subdoctrine might unlock an army spirit that increases bayonet strength.
I hope the rework surprises you in a positive way. There’s more to polish, so expect iterative changes as we continue development. I’ll be monitoring feedback and answering questions as we move forward.