You know, military intelligence.
Without the German navy's B-Dienst, no practically clairvoyant intercepts by Karl Donitz's U-boats of allied transatlantic convoys. Without "inexperienced, tired or lazy" German Enigma machine senders, so much the worse for allied efforts at Bletchley to break the encipherment keys that proved so crucial to the allied prosecution of the war. Without "Magic," no penetration of Japanese naval and diplomatic ciphers.
Heart of Iron 2 modeled some of this stuff in terms of basic encryption/decryption, radar, spies, sabotage, propaganda, and assassinations, but Heart of Iron 3 looks to bring the concept center-stage.
According to design lead Johan Andersson
The radar station is no longer just a radar station but is now an intelligence-gathering site. The radar station is now also a signal intercept and analysis station, giving you (and the bad guys, mustn't forget about them) the ability to peer behind enemy lines. The bigger the radar station, the better you are at doing this.
How does this sort of thing affect the game? Says Andersson
...we now have an increasingly incomplete picture of what is going on behind enemy lines... you are not just asking yourself where the enemy is but you also need to ask the question how good is my intelligence?
Andersson claims this fundamentally alters the way the A.I. "thinks" strategically.
Now the AI can look behind enemy lines without having to resort to any of those crutches that annoy players so much. The AI can start to react to things like a build of allied troops in Southern England (could this be Overlord?) within exactly the same rule mechanics that a player is operating in.
Tantalizing, sure, but did we really need Hearts of Iron 3 to gets even more granular? Hearts of Iron 2 was fine-grained enough, what with its abstract military doctrines and leader traits and social engineering shifts and exhaustive lists of historical research teams you can assign to bake up technology ranging from isotope separation to centimetric radar to agricultural chemistry.
Paradox's development team says they're in fact working to grind down the game's learning cliff.
Time for that "Learning Curve" development diary update?