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Nuclear Bombs (Draft, 1.8)

Nuclear bombs are a late-game mechanic in Hearts of Iron IV.


Deploying nuclear bombs needs the right technologies from Engineering technology, a bit of infrastructure, and investment into air power over the target.

The first technology, Atomic Research Atomic Research.png, gives a -2% research time reduction.

The second technology, Nuclear Reactor Nuclear Reactor.png, unlocks the state level building State buildings.png titled "Nuclear Reactor" Nuclear reactor.png which can be found in the Construction screen. Built nuclear reactors provide the state with enriched uranium for use in nuclear weapons, but have no effect without the requisite technology to make nuclear bombs. However, it may be wise to build a few reactors before finishing the engineering technology Nuclear Bombs due to the long reactor build times.

The final technology, Nuclear Bombs Nuclear Bombs.png, allows the country to produce and stockpile nuclear bombs. Each reactor will provide approximately 1 bomb per year. The bomb production progress can be seen via a slowly progressing percentile bar. More reactors will produce more bombs, up to and exceeding 1 per year. But at some point they will stop being usable.


All of the major powers and minors, except Japan Japan.png, have focus trees with an option to acquire nuclear technology at a significant reduction in research time. This can be used to substantially reduce the ahead-of-time research penalty. These national focuses have names such as The Manhattan Project, Nuclear Effort, The Maud Committee, Research City Experiment, Wunderwaffe, and Secret Weapons.

If the game is set to historical national focuses and the AI is left to play the major powers, then only Germany German Reich.png and the US United States.png are likely to have all of these technologies unlocked on or before 1945; the USSR Soviet Union.png, United Kingdom United Kingdom.png, and France France.png should soon follow.


Nuclear Bombs are deployed onto specific provinces. In order to deploy a bomb, the following requirements must be met:

  • at least 1 bomb must be available (look for the "radioactive" Nuclear bomb availability.png icon at the top of the game's main screen)
  • hostile with the province controller
  • at least 75% Air superiority
  • a Strategic Bomber in range of the province (despite having the strategic bombing mission, tactical bombers cannot deliver nuclear bombs)
  • once ordered, it will take 12 hours for the nuclear bomb to detonate. however multiple nuclear bombs can be dropped in parallel


  • Does anywhere from 10%-90% damage to the current strength of any divisions in the nuked province (Defines NUKE_MIN_DAMAGE_PERCENT and NUKE_MAX_DAMAGE_PERCENT)
    • Ex: If a division has 10 strength the nuke will do anywhere from 1-9 damage to strength, even if the possible strength of the unit is higher.

(REPLACING) While the effects are primarily focused on the target Province, there is some effect onto the whole state and even country:

  • Divisions in the province will be reduced to 20% or less of their strength and organization
  • all province buildings will be heavily damaged
  • statewide buildings will be heavily damaged, which will affect both sides
  • statewide buildings present in a province will only be affected if they are the direct target
  • planes in an airfield might be wiped out nearly completely
  • war support for the target will be dropped by up to 20%, scaled to (intact?) infrastructure in the province
    • this will be reduced if not at least 3 victory points are in the affected province
  • it also reportedly provides some surrender progress
  • The first use, as well as uses on specific (capital) cities, will result in news messages. However those are purely informational
  • After the 2nd nuclear bomb has been dropped on a Japanese core state, Japan Japan.png has a special decision for surrender