After the lukewarm reception of Hearts of Iron III, Paradox set out to address as many criticisms of the base game as possible with their first expansion. The main features are as follows:
- Definable Theaters of War - One of the biggest complaints was that you could not create your own theaters, instead relying on the AI to manage the pre-defined ones. Now, you can create new theaters yourself, and assign AIs to them separately. This allows you to more easily manage multiple fronts or perhaps wide fronts shared with multiple enemies.
- Order of Battle Browser - The new OOB browser allows you to effortlessly rearrange your forces across multiple theaters.
- Hidden Victory Conditions - At game start, each faction leader (Axis, Allies, Comintern) picks their own set of victory conditions hidden from everyone else. This leaves players second-guessing eachothers motives at every turn, and allows repeat playthroughs to play differently.
- New 1940 scenario - Start the game just before the Fall Gelb, the Invasion of France.
- Hundreds of new events - Many new events were added to increase historical flavor.
- Improved AI - The AI has been improved in all areas. The theater AI can be given separate stances for land, air, and sea, military AI is improved with better in-depth-defence tactics and multi-stage invasions and diplomatic and production AIs have been improved to make countries act more in tune with their real world historical counterparts and build more appropriate units.
As of the 23rd December, 2010, Semper Fi is a download-only expansion.
Operating system: Windows 2000/XP/Vista
Processor: Intel Pentium IV 2.4 GHz or AMD 3500 (quad core)
Memory: 2Gb RAM
Hard disk space: 2GB HDD space
Video: NVIDIA GeForce 8800 or ATI Radeon X1900 videocard
Sound: DirectX-Compatible soundcard
DirectX®: DirectX 9.0c or more