The Götterdämmerung expansion transforms late-war warfare and secret scientific research in Hearts of Iron IV. Centered on Germany, Austria, Belgium, and the Congo, the expansion replaces abstract late-game technology trees with dedicated Special Projects Facilities, historical Wunderwaffen super-weapons, and tactical military Raids. Major powers can now build map-placed Experimental Facilities, deploy V-2 ballistic rockets, build nuclear atomic reactors, and dispatch commando teams to sabotage enemy research facilities.
What this covers: Special Projects Facility management, the four scientific specializations (Nuclear Research, Aerodynamics & Avionics, Land Warfare, Naval Engineering), Raids tactical interface, and covert sabotage. Why it matters: Constructing atomic bombs and V-weapons now requires physical Experimental Facilities that enemies can pinpoint and bomb into rubble. Who should pick this: Generals planning late-game 1944-1945 tactical breakthroughs against entrenched superpowers.
Special Projects Facilities and Scientists
Rather than spending generic research slots on secret weapons, major nations construct physical Special Projects Facilities on the map:
| Project Discipline | Landmark Breakthrough | Required Resources & Infrastructure | Strategic Impact |
|---|---|---|---|
| Nuclear Research | Atomic Bombs & Nuclear Power | Map-placed facility hooked to the supply network and staffed by a lead scientist; bomb projects require the Nuclear Reactor project, and some projects consume resources while they run | Devastates enemy industrial capacity, forces unconditional surrenders |
| Aerodynamics & Avionics | V-1 Flying Bombs & V-2 Rockets | Map-placed facility; breakthroughs earned from aircraft, rocket and radio research | Long-range strategic bombardment immune to fighter interception |
| Land Warfare | Land Cruiser (Landkreuzer P. 1000 Ratte) & Super-Heavy Railway Gun | Map-placed facility; the railway gun project spawns its gun on completion, named Dora for Germany | Unstoppable breakthrough spearheads on narrow frontlines |
| Naval Engineering | Nuclear Submarines & Air-Independent Propulsion | Map-placed facility; the Air-Independent Propulsion project unlocks the High-Speed Walter Engine submarine module technology | Strangles Allied Atlantic convoys with advanced submarine designs |
Each facility is staffed by recruited historical scientists (such as Wernher von Braun or J. Robert Oppenheimer) whose personal traits accelerate specific breakthroughs.
Earning Scientific Breakthroughs
A Special Project cannot simply be bought with a research slot. Each one is gated behind scientific breakthroughs for its category, and there are six documented ways to earn them:
| Breakthrough Source | Daily or Per-Event Gain |
|---|---|
| Capturing an enemy Experimental Facility mid-project | +10% breakthrough progress for the matching category, then reduced by 60% for each further capture of that category |
| Rocket sites and nuclear reactors | +0.01% Aerodynamics and Avionics per site per day, or +0.01% Nuclear Research per reactor per day |
| National focuses | Category progress from specific focus branches on some countries |
| Prototype iterations | Some prototype outcomes add breakthrough progress to their own category |
| A scientist performing basic research | +0.05% times the scientist’s skill, with a 0.5 times diminishing return for each scientist beyond the first |
| Researching related technologies | +0.12% per research slot per day while those technologies are being researched, regardless of research speed bonuses |
The last row is the one players underestimate: raw time and research slots spent on a category’s supporting technologies matter more than the speed at which those technologies finish, so a nation that parks several slots on armor and artillery is quietly banking Land Warfare breakthroughs long before it ever opens a facility.
The Three Phases of a Special Project
Every project moves through an establishing phase, an initial research phase and a prototyping phase. The establishing phase repeats each time the project is started or restarted, the initial research phase only needs to be cleared once, and the prototyping phase is the long grind, generating successive prototypes until overall progress reaches 100%. Each finished prototype adds a random amount of progress and can fire an outcome — some positive, some negative, and some that force a decision, such as an Espionage Threats event that lets a player trade security for either research speed or scientist experience.
The facility itself is a target. Experimental Facilities consume 3 supply each, and a resource shortage or a supply shortfall can throttle a project’s speed down to 0.2 times; a facility with less than 66% of its supply needs met shows a warning in the research screen. An injured lead scientist stops project progress entirely until reassigned, and a damaged facility pauses all of its projects until repaired. Capture matters in both directions: losing a facility mid-project costs up to −20% of current progress, while capturing an enemy facility that is further along hands over 20% of the progress difference. Cancelling a project is not immediate — it takes 10 days to actually stop, during which the facility still consumes resources and can still be captured, and it cannot begin a new project until the old one has fully stopped.
Executing Military Raids
The new Raids Interface allows nations to plan surgical military strikes without declaring total ground offenses:
- Target Selection: Identify high-value enemy assets — ports, industrial structures, research facilities, special resource collection areas, or the dams and canal locks targeted by the Bouncing Bomb project’s Dam and Lock Bombing Raids.
- Preparation Phase: Allocate special forces commandos, air transport wings, and clandestine intelligence assets to build raid planning to 100%.
- Execution: Launch the raid. A successful operation sabotages the facility, setting enemy nuclear or rocket research back by months while inflicting catastrophic morale penalties.
Defending Against Strategic Sabotage
Because your own rocket silos and atomic reactors can be raided by Allied paratroopers or bombed by British Lancasters, defensive security is vital:
- Construct state-of-the-art Flak Towers and Radar Arrays directly around facility provinces.
- Station elite military police garrisons in adjacent urban centers to intercept enemy espionage infiltrators before they compromise secret blueprints.
The Landmark Wunderwaffen Projects
The Special Projects list is short and specific, so it pays to know what each discipline actually unlocks before committing a facility to it. Land Warfare, for instance, is where the heaviest hardware lives.
| Project | Prerequisite Chain | Completion Effect |
|---|---|---|
| Land Cruiser (Landkreuzer P. 1000 Ratte) | With No Step Back: Super-Heavy Tank Chassis | Unlocks the Land Cruiser Chassis and its module set, or adds a Land Cruiser and a production line at 35% completion |
| Super-Heavy Railway Gun | Railway Gun technology plus No Step Back | Spawns one Super-Heavy Railway Gun, named Dora for the German Reich |
| Super-Heavy Howitzer | Towed Artillery plus Götterdämmerung | Unlocks the Super-Heavy Howitzer and, through it, the Self-Propelled Super-Heavy Howitzer |
| Multi-Charge Large Caliber Gun | Super-Heavy Howitzer plus Götterdämmerung | Unlocks construction of the V3 Multi-Charge Large Caliber Gun |
| Stronghold Network | Basic Fortification plus Götterdämmerung | Advanced fortification content, with outcomes that can prevent tunnel collapses or grant fortification research bonuses |
The Land Cruiser is the project’s headline for a reason. Its historical counterpart, the Landkreuzer P. 1000 “Ratte”, was a Krupp design for a 1,000-tonne tank, roughly 35 metres long and 11 metres tall, to be armed with a dual 28 cm naval gun turret and driven by naval diesel engines; Adolf Hitler approved development in 1942, but Albert Speer cancelled it in early 1943 before a prototype existed. HoI4 turns that cancelled design into a late-game super-heavy with its own chassis and module set, while the Super-Heavy Railway Gun simply hands the player the completed gun on completion — and names it Dora if the country is the German Reich.
Nuclear, Naval and Air Projects to Plan Around
The other three disciplines follow the same rule that one project can require an earlier project to finish before it opens. In Nuclear Research, the Atomic Bomb work runs through the Nuclear Fission Bomb Project, which must follow the Nuclear Reactor project, and the later Thermonuclear Bomb requires the Nuclear Fission Bomb, MRBM and Nuclear Warheads first — at which point the branch also unlocks the Medium Range Nuclear Missile. The Nuclear Engines project unlocks the Nuclear Submarine Reactor, Nuclear Heavy Ship Reactor and Nuclear Carrier Reactor ship modules, tying the nuclear tree directly into the naval one.
Naval Engineering is where the anti-convoy designs sit: Fleet Submarine and Cruiser Submarine open the submarine hulls, Nuclear Submarine and Missile Launching Submarine unlock the modern boats and their missiles, and Air-Independent Propulsion unlocks the AIP module that gates the AIP-Diesel Combination Engines technology. Aerodynamics and Avionics covers the aircraft and rocket side: the Bouncing Bomb project unlocks the Dam Bombing Raid and Lock Bombing Raid used by the raids interface, the Flying Bomb project (The V1 Project) develops guided-missile technology, the Ballistic Missile project (The V2 Project) opens ballistic missiles under Götterdämmerung, and the Intercontinental Bomber branch leads toward the Amerikabomber. Because breakthroughs are earned from the technologies supporting each category, a late-war Germany that has spent the whole game in armor and artillery is naturally closer to the Land Warfare landmarks than to the nuclear ones.