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Hearts of Iron IV
Hearts of Iron IV
Jun 4, 2026
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Dev Diary | HOI IV-X Anniversary Update

4/5 Significant

Hearts of Iron IV celebrates its 10th anniversary with a massive 'War Effort' patch featuring a total naval rebalance, significant late-game performance optimizations, and reworked Naval AI templates.

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Key Changes

  • 1Massive Naval Rebalance (Manpower, Range, Resource Costs)
  • 2Late-game Performance Optimizations (RTTI, Sound Pool, Supply)
  • 3Naval AI Rework (Templates for major powers, better retreat/repair logic)
  • 4Nationalist China Focus Tree Buffs (21 focuses reduced to 35 days)
  • 5New 'Steiner!' Achievement for Germany
  • 6Submarine Stealth and Survivability Buffs
  • 7Carrier Combat and Strike Multiplier Buffs
  • 8International Market and Lend-lease QoL Improvements
  • 9Heavy MG Fighter IC Cost and Reliability Nerfs
  • 10Nine-Powers Treaty Event and AI Logic

All Changes

⚓Naval Balance(20)

  • nerfNavy: Naval Minimum Chance to Hit reduced from 2% to 0.5%.
  • buffNavy: Supply Consumption reduced for Carriers (1.2 to 0.8), Battleships (0.8 to 0.56), Battlecruisers (0.48 to 0.32), and Heavy Cruisers (0.4 to 0.24).
  • buffNaval Modules: Removed Resource Costs from most naval modules including guns, deck armor, and hangar decks.
  • buffDestroyer: Destroyer Naval Range increased across all tiers (Early: 2000km, Basic: 2500km, Improved: 3000km, Advanced: 3500km) and service manpower reduced for Basic, Improved, and Advanced hulls.
  • changeCruiser: Cruiser Hull costs increased (Early, Basic, Advanced) and Range reduced (Improved, Advanced), while service manpower was reduced across the board.
  • changeHeavy Ship: Heavy Ship Hull costs increased (Early to Advanced) while service manpower and fuel consumption were reduced across all tiers.
  • changeCarrier: Carrier Naval Range increased and service manpower/fuel consumption reduced, though hull costs increased across all tiers.
  • buffSubmarine: Submarines now hide faster (8h vs 20h) and stay revealed for less time (12h vs 16h) at the start of combat.
  • buffSubmarine: Submarine Visibility reduced for Early, Basic, and Improved hulls, and visibility penalties from Positioning and Shallow Waters were significantly lowered.
  • buffSubmarine: Submarine Engines II, III, and Nuclear now provide visibility reductions; Nuclear engine speed bonus increased to +20%.
  • buffCruiser: Cruiser Ship Engines I-IV production costs reduced; Engine I speed bonus increased to +25%.
  • changeHeavy Ship: Heavy Ship Engines I-IV production costs reduced and speeds increased, though fuel consumption increased across all tiers.
  • nerfCarrier: Carrier Ship Engines I-IV naval speed reduced and fuel consumption increased across all tiers.
  • buffEscort Carrier: Escort Carrier IC cost reduced (1500 to 1250), manpower reduced (2500 to 1500), and fuel consumption reduced, while detection bonuses increased.
  • buffPanzerschiff: Panzerschiff manpower, IC cost, and surface visibility reduced, though hull cost increased by 1 Chromium.
  • buffCoastal Defense Ship: Coastal Defense Ship significantly buffed: manpower, IC cost, Steel cost, and visibility reduced, while HP and Range increased.
  • changeNavy: Rebalanced naval retreat mechanics: increased base escape speed and combat duration scaling, while capital ships now retreat at half their usual strength threshold.
  • buffCarrier: Increased NAVAL_STRIKE_CARRIER_MULTIPLIER to 12.0 and CARRIER_COMBAT_DAMAGE_STATS_MULTIPLIER to 0.5.
  • changeNavy: Naval XP Gain for Patrol, Convoy Raiding/Escort, and Mine missions set to 0.2, and Strike Force to 0.05.
  • buffNavy: Navy Mastery gain increased for Strike Force (0 to 0.05) and Convoy Raiding (0.2 to 0.3).

🏆Gameplay & Achievements(5)

  • newAchievements: Added 'Steiner!' achievement: As Germany, reach 30% surrender progress after June 22, 1941 while at war with USSR, France, and UK, then control Moscow, Paris, and London.
  • nerfFighter: Heavy MG Fighter IC cost increased (2x +20%, 4x +30%) and 4x mounts reliability reduced by 2.5%.
  • nerfNavy: Screening bonus now scales with efficiency; partially screened formations no longer receive the full bonus against capital fire.
  • changeCarrier: Carrier Sortie Settings now only apply to the first 24 hours of Naval Combat.
  • newDiplomacy: Added an event for signatories of the Nine-Powers Treaty when China is attacked.

⚙️Performance & Stability(5)

  • fixPerformance: Removed RTTI overhead in release builds by using static_cast, improving performance for all reference pointer dereferences.
  • fixPerformance: Implemented a sound pool system to keep effects in memory for ~20 seconds, reducing file system access and stuttering.
  • fixPerformance: Optimized late-game performance by speeding up fuel calculations (90% faster), airwing accident checks, and equipment data compaction.
  • fixPerformance: Fixed performance degradation in massive naval battles involving over 1,000 ships.
  • fixPerformance: Added caching to root and fallback orders, significantly speeding up unit code and army selection performance.

🧠AI Improvements(6)

  • changeAI: Reworked naval ship templates for Italy, England, USA, and Japan to follow a historical four-tier scheme (Early to Advanced).
  • changeAI: Germany AI will now prioritize building submarines over surface ships to match historical doctrine.
  • buffAI: AI now reserves more dockyards for repairs and will continue repairing until critical damage is resolved.
  • buffAI: AI will train troops and fleets more frequently and opportunistically, but will avoid training divisions adjacent to enemies.
  • buffAI: Strike forces can now target ongoing combats while exiting their own and will ignore active combats on the way to a valid target.
  • changeAI: Italy AI now commits fewer units to the Alexandria push to hold Africa longer; UK Alexandria defense buffer slightly reduced.

🗺️National Focuses(2)

  • buffNationalist China: Reduced focus time from 70 to 35 days for 21 focuses across Industry, Army, Air, Navy, and Politics branches for Nationalist China.
  • buffNationalist China: Moved 'Construct the Banqiao Dam' earlier in the Nationalist China focus tree.

🖥️UI & Quality of Life(5)

  • newUI: Added 'Repair-now' button to fleets which stops current missions to prioritize repairs.
  • buffUI: International Market now defaults to maximum equipment selection and automatically sets the minimum acceptable civilian factory count.
  • buffUI: Lend-lease now defaults to maximum amounts the receiver can handle and features improved UI logic for 'once' and 'percentage' modes.
  • newUI: Added ability to filter divisions by type in the division overview window.
  • newUI: Added 'Hit Profile' stat display to the Ship Designer and Ship Cards.

🐛Bug Fixes(4)

  • fixStability: Fixed various crashes related to order invalidation, carrier airplane deployment, and late-game scientists.
  • fixBritish Raj: Fixed several British Raj focuses including 'Mixed Economy' and 'Acquire new Resources' to correctly apply resources.
  • fixNavy: Fixed a bug where a ship would gain strength through doctrines but appear damaged upon reloading a save.
  • fixAir Force: Fixed a bug where planes destroyed by static anti-air or raids did not count toward war participation.

📅Coming Soon(2)

  • newDLC: Thunder at Our Gates DLC release scheduled for June 11th.
  • newCommunity: Anniversary 'behind the scenes' video and teaser of upcoming content scheduled for June 18th.

Summary

The 10th Anniversary Update (v1.18.3) focuses on a comprehensive overhaul of naval gameplay, adjusting everything from ship manpower and range to resource costs and combat multipliers. Late-game performance has been significantly improved through technical optimizations like RTTI removal and sound pooling. Additionally, the Naval AI has been reworked for major powers to follow historical ship templates and exhibit smarter strategic behavior. The patch also introduces a challenging new achievement for Germany and significant buffs to the Nationalist China focus tree.

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