The new expansion Hearts of Iron III: Their Finest Hour will improve many areas of the game. Expanded espionage system with new and reworked missions including new covert operations that can be performed on the map and new battle plans mode where you can load historical plans, draw your own and share with allies in real-time during multiplayer.
Features
New unique elite units for each major nation's army - Ghurkhas, Rangers, Imperial guards etc.
Deeper naval invasions system with the possibility of developing specialized landing and assault crafts to improve effectiveness.
More detailed control over strategic warfare and a generalized lend-lease system for lending your industrial might to allies.
Leaders are now able to gain traits and allocating them is more important than ever with a new combat tactics system.
A new custom game mode for single and multiplayer where you start with a clean slate and can instantly produce units, research technologies and affect political alignment, speeding up the early years for those who would like to jump straight into the action.
Two new detailed battle scenarios, the Finish Winter War and the Spanish Civil War
Source: The Publisher Website.