Unlike many previous Ace Combat titles, Assault Horizon does not set the story in the fictional world, but on a future Earth. The player gets to fly and fight over known seas and cities such as Miami (USA), Dubai (India) or Moscow (Russia). While the basic flying controls are kept, there are many new upgrades and innovations to the known warfare in the series. One is dogfighting where you can tail behind the enemy plane and keep it close to your machine gun. The tailing sequence remains active as long as you can keep up with the enemy fighter, until he is no longer visible on the screen. You can punch the thruster to shorten the distance and make your shots more accurate and destructive. There is also a way for the enemy plane to tail you, even when you are tailing another plane. In such case you can try to outmaneuver it or hit the breaks and make a spin to quickly come up behind it and switch the roles of hunter and hunted. Another addition is the bombing run which lets you enter the bombing zone for a more detailed and easier assault against the ground targets and vessels.
Next to fighters the player gets to fly heavy bombers, commandeer a gatling gun on a chopper or fly an Apache helicopter, which changes change the warfare from previous titles. With heavy planes you can provide artillery assistance to your ground troops from way up in the sky, and zoom in based on the type of cannon you are using. With helicopters, on the other hand, you will use different tactics such as flying below rooftops to avoid enemy SAM sites and generally be closer to the ground troops of infantry and tanks.
While the story is centered around Lt. Colonel William Bishop, the leader of the Warwolf squadron, you will get to control different characters depending on the mission at hand, since the Colonel is an ace pilot and is not so skilled at flying helicopters or heavy bombers. You are part of the UN forces composed of both NATO and Russian military, fighting against an insurgent group of unknown forces and goals. As in previous games in the series, there are many known modern fighter planes to select from. F-14 Tomcat, F-15, F-16, F/A-18 Hornet, MIG 21 and MIG 29 are but a few, and you can also unlock more planes and even colors as you play.