Hearts of Iron II: Doomsday contains everything that was in the original game while highlighting and expanding the period after historical World War II including a hypothetical nuclear war between the Soviet Union and the Allies. The expansion pack features among other things a reworked intelligence model (which allows the player to use espionage sabotage and other things in an "intelligence page" accessible through the main screen) improved AI and a scenario editor.Doomsday also features some other changes and additions such as:*Additional graphics such as bomber sprites*Escort Carriers*Hospitals that recover manpower losses*A "do not upgrade" button for divisions*The option of automating the production sliders*Submarines have separate stats for convoy raiding and naval combat*An extended timeframe — the game end date has been changed to 1953*New technologies to bring the game into the cold war era*An included scenario editor*The ability to trade divisions between nations*The ability to attach escorts while recruiting divisions