Zone Of Endless.
An Artificial Intelligence program initiated by the Belkan Greymen and Gründer Industries that covertly gathered data during the 1997 Usean Coup d’etat.
There is no ADF-1 Falken in Assault Horizon, but the Shinden II works as a nice looking substitute IMO.
It is suggested that the Usean Rebels captured the Z.O.E. prototypes, including the ADF-01 FALKEN.
However, I would propose that they were actually still under the control of the Belkans and simply mascurading as Usean rebel forces.
Consider if you will that the Usean rebel pilots don’t seem to know anything about them, which is particularly highlighted when the Z.O.E. F/A-18E Super Hornet appears during the engagement between the Scarface and Cocoon Squadrons.
The leader of Cocoon Squadron, Camilla “Catwalk” Almeida specifically asks if the Z.O.E. aircraft is with the allied forces. The only response is that it is using a Rebel IFF code, but that alone does not mean it is actually operated by them.
So why is Z.O.E., and by extension the Belkans, so interested in Phoenix?
I would put forth the possibility that Phoenix could, in fact, be Cipher.
The origins of the Z.O.E. program is in the data recovered from the dogfight between Cipher and Larry “Solo-Wing Pixy” Folke at the end of Ace Combat Zero.
Cipher subsequently disappeared completely after the Belkan War, as if he never existed.
The games narrator even states during the ending that its doubtful he actually existed at all.
That’s actually unusual for an Ace Combat protagonist.
There are no doubts that Mobius 1, Garuda 1 or Gryphon 1 existed and even continued to serve following the end of their respective games (Blaze and the Razgriz is a bit more ambiguous, but that’s all part of the story in itself).
It would not be beyond the realms of possibility that the battle with his former wingman and buddy left Cipher, aka the Demon Lord, troubled enough to abandon this identity.
Enter “Phoenix”. A skilled and experienced mercenary pilot who appears almost immediately after Cipher vanishes.
The call sign itself means rebirth.
Now Cipher was possibly the greatest ace to have ever flown the skies of Strangereal. His track record against the elite squadrons of the Belkan Air Force, “A World Without Boundaries” and taking out Solo-Wing Pixy’s ADFX-02 Morgan in a lowly F-15C.
Feats that call into question the achievements of the other protagonists in the series.
Z.O.E. needed data from the greatest aces, data that had it’s origins with Cipher.
If the Belkan’s realised that Cipher = Phoenix, then it would make even more sense for the Z.O.E. to go out of it’s way to engage Phoenix and continue gathering data from the pilot that crushed the best that the Belkan Air Force had to offer.
Yet it was never enough to beat the original.
Just a theory