Thunder at Our Gates is, as of this guide, Hearts of Iron IV's most recent Theater Pack, released in June 2026. Like all Theater Packs, it doesn't rewrite the whole game's mechanics, but it does bring two additions that affect any game, plus new content for three Pacific nations.
New Nations
The pack adds focus trees for Australia, Siam (Thailand) and Indonesia — three nations that until now had very limited development within the Pacific theater. It's part of Expansion Pass 2, entirely focused on that region, alongside No Compromise, No Surrender and Peace for Our Time.
Army General Headquarters
The most significant mechanical addition is Army General Headquarters (HQs): a command layer between your divisions and the general high command, affecting the coordination and logistical support of army groups. It's a mechanic that touches any nation, not just the three new ones, so it's worth understanding even if you're not playing in the Pacific.
Ship Captains
The second mechanical addition is ship captains: naval officers with their own traits that you can assign to your fleets, similar to land generals. It adds a layer of customization to games with a strong naval component.
Is It Worth Buying?
If you usually play European powers and aren't interested in the Pacific theater, the new nations won't pull you in directly — but Army General Headquarters affects any game, so the pack isn't purely cosmetic for the rest of the world. If you're also interested in Australia, Siam or Indonesia, it's a fairly clear buy.