Blue on Blue is the fifth mission of Ace Combat: Assault Horizon.
After a successful mission alongside Spooky 01, Warwolf Squadron prepares to land at the NATO air base. However, the ten-plane Big Bear Squadron, led by Ivan Stagleishov, abruptly takes off, causing a near collision with William Bishop. Kingmaster reports that the SRN is attacking the nearby city of Carruth, and all available units are being scrambled.
Warwolf and Lion Squadrons engages a squadron of Fishbeds heading towards the base. During the battle, Kingmaster asks Bishop to contact Stagleishov and ask him for a situation report. The General vaguely replies: "We're heading in your direction". He then ceases further communication after being pressed. Shortly afterwards, Big Bear reappears and begins attacking Lion and Warwolf. With no further communication from Stagleishov, Bishop authorizes all planes to return fire on the Russians. Big Bear's MiG-29s are much more maneuverable than any aircraft fought before, and will often preform a Counter-maneuver when pursued. After much of Big Bear Squadron is shot down, General Stagleishov will finally contact Bishop. He regrets that the squadron was unable to kill him, and claims that his betrayal was done of his own accord.
Afterwards, a Su-35 with a shark's mouth painted on the nose, the same aircraft from Bishop's nightmare, appears and begins to pursue Guts. Bishop engages the enemy plane, but the pilot is extremely agile and almost instantly position himself behind Bishop. Eventually, Bishop will be hit by one of his foe's missiles. After taking a hit, Stagleishov commands the enemy pilot, calling him "Markov", to cease attacking. Bishop regains control of his plane and commences an emergency landing. General Pierre La Pointe will inform Bishop that the men in the base's control tower were found dead, and Kingmaster's transmissions claiming that Carruth was under attack actually came from Big Bear. Major Sergei Illich has also taken command of the remaining loyal Russian pilots. Bishop's landing gear malfunctions and his plane crashes into the runway. He steps out it only to witness the destruction of Carruth by a massive explosion.
- When you engage Markov, he seems to warp the mechanics and balances that the player abides by in DFM mode. He is capable of counter maneuvering at will, whether he is leveled off or not. Bullets and Missiles seem to only cause minimal to no damage at all. The Player can not counter his counter maneuvers since the icon for it does not appear. Also if he manages to fire a missile before you Counter Maneuver, the missile will always hit whether you pop flares, activate an ECMP, counter maneuver again, or all three at the same time. This can be easily described since Bishop is scripted to lose.
- When landing, the front gear will always collapse, even if it never touches the ground.
- The term "blue on blue" is the NATO designation for friendly fire. In this case, the moment Big Bear Squadron attacks Task Force 108.