The game features both a single-player mode as well as a multiplayer mode supporting ad hoc and Infrastructure mode. The game features a co-operative campaign which can be played with up to four players as well as a competitive multiplayer mode supporting up to eight players. Some missions in the campaign will make use of the Joint Assault Mission System, which breaks the players into teams and has them coordinate attacks where each effort can affect the other team's situation. A new feature of the game is the Enhanced Combat View mechanic, which removes the distanced fighting seen in almost every flight simulation game.
Joint Assault features more than 40 licensed aircraft types, plus fictional aircraft from previous installments in the series, particularly Ace Combat X: Skies of Deception. Propeller planes will also be available for the first time in the series, with players being able to unlock the F6F-5 Hellcat and the A6M Zero. Frequent use of each aircraft allows the player to unlock more weapons, tune-up parts, paint schemes, and new emblems. The game's official superfighter is the GAF-1 Varcolac.
Players assume the role of a pilot freshly hired by a private military company called Martinez Security. The unnamed pilot is assigned to Antares Squadron under the command of Major Frederick Burford. Another squadron within the company, Rigel, has Milosz Sulejmani, Daniel Oruma, Faryd Gaviria, and Kiriakov. The game's antagonists are Col Nicolae Dumitrescu and international insurance businessman Andre Olivieri.
The game is set sometime after the global financial crisis. Off Midway Island, the player begins his first day on the job flying with Martinez Security in an exercise involving the US 7th Fleet and the Japan Maritime Self-Defense Force. After a successful practice run, several unidentified bandits suddenly appear from the east and head due west. Burford breaks the news that the bandits, now known as the "Valahia," are attacking Tokyo and the 7th Fleet is seeking Martinez Security's help. The defense of Tokyo is a success, with the destruction of the Valahia's Orgoi flying fortress and heavy damage being dealt to a larger airborne fortress called the Spiridus. Antares Squadron also helps the SDF fend off Valahia attacks at the Boso Peninsula and over the Izu Islands. In the midst of the action, the Rigel Squadron defects to the Valahia and leave Tokyo upon considering a lucrative offer by leader Col Nicolae Dumitrescu.
Embarrassed by the defection, Martinez Security joins the International Union Peacekeeping Force (IUPF) in stopping all Valahia activity around the world, starting with operations in the Middle East and the Balkans. During missions over Croatia and Serbia, the player fends off an attack from Rigel Squadron, now calling themselves the Varcolac Squadron. The crackdown is given an added boost when the IUPF destroys the Spiridus over London. Dimitrescu later announces that the Valahia have captured several ex-Soviet ballistic missile silos in Central Asia. As the IUPF prepares to attack the silos, Antares Squadron is hired to pilot Andre Olivieri's personal Boeing 747-200B over Valahia-controlled territory.
As Antares Squadron destroys the silos and eliminates the Valahia threat, the player discovers that Olivieri used his insurance earnings to finance the Valahia and the IUPF's operations, preparing for an operation named Golden Axe, scheduled to take place over San Francisco. It is revealed that the attacks themselves are part of a plan for Olivieri to establish a monopoly over the global insurance market. He also orders the Valahia eliminated because they went rogue on him with plans to establish a new nation. Antares Squadron, which reorganizes at Midway after the silo attack, is also attacked by the Golden Axe forces in an attempt to prevent them from stopping the operation.
In a final series of missions over Nevada and the Bay Area, Antares engages the rest of the Golden Axe forces and the Varcolac Squadron. After eliminating the Varcolac team, the player is sent to destroy Olivieri's underground data center at his company's headquarters in downtown San Francisco. The data center is destroyed, and Olivieri is killed in the blast, ending any further schemes of the Golden Axe Plan to foment more conflict.
In the aftermath of the Battle of San Francisco, Olivieri's plans are exposed to the public, and the Antares Squadron continues to defend the skies.
The game was officially announced by Namco Bandai on January 12, 2010, however screenshots had been leaked a day before on IGN. The game officially went gold on August 13, 2010.
Reception to the game has been mixed. GameSpot and IGN  stated that the game's story was not as dramatic as those from previous titles, and its saving grace is the co-operative play options and the easy access to new rewards. Gamesradar cited the PSP's control options as a letdown compared to console versions, but lauded the Joint Assault system as an idea worth seeing in future games, especially with Assault Horizon. GameFan reviewer Christopher Bowen said the campaign was tedious and the online cooperative system is better off on the console versions. G4tv.com gave the game a 4/5 score.
- Chris Roper (January 11, 2010). "Ace Combat: Joint Assault Announced". IGN. Archived from the original on 15 January 2010. Retrieved January 15, 2010.
- Jump up^ Namco Bandai (January 12, 2010). "Namco Bandai Games America Announces Ace Combat Joint Assault for the PSP". IGN. Archived from the original on 21 January 2010. Retrieved January 15, 2010.
- Jump up^
- Jump up^ http://www.gamespot.com/psp/action/acecombatjointassault/review.html
- Jump up^ http://psp.ign.com/articles/111/1119640p1.html
- Jump up^ http://www.gamesradar.com/psp/ace-combat-joint-assault/review/ace-combat-joint-assault-review/a-2010083114543610065/g-20100112103642747082
- Jump up^ http://diehardgamefan.com/2010/09/08/review-ace-combat-joint-assault-sony-psp/
- Jump up^ http://g4tv.com/games/psp/63302/ace-combat-joint-assault/index/