The phrase "acknowledged enemy" is correct and usable in written English.
It can be used to refer to an opponent or adversary that is recognized or accepted as such, often in a context of conflict or rivalry.
Example: "In the ongoing negotiations, we must consider our acknowledged enemy and their strategies."
Alternatives: "recognized adversary" or "accepted foe".
What few people know, however, is that Clausewitz warned that if the enemy's "Schwergewicht" (center of gravity) -- both political and military -- cannot be located or fully destroyed, the result could be a "formenloser Krieg" (a formless war), a conflict without acknowledged enemies and stated war-aims.
In countries like those, U.S. military leadership has acknowledged that enemies such as al-Shabab and the Taliban can't be eliminated by killing every last member.
While initially silent on the Stuxnet sabotage, President Mahmoud Ahmadinejad eventually acknowledged that "enemies" had been successful in "making problems" by installing computer malware in industrial switches used to control the centrifuges, making them spin out of control at high speed.
Richie's assistant, studiously, loyally BlackBerrying on the couch, refused to acknowledge the enemy presence.
At the highest levels of the Administration, the notion of acknowledging the enemy's grievances was dismissed as defeatist.
She implies that she's a secret adviser to her ex-husband, and when she does insult our President it's in the passive manner of a woman acknowledging an enemy at a luncheon: "I was too successful to be Mrs. Trump," she writes.
The group's skill at manipulating social media, for recruitment and projection of power, has been acknowledged even by enemies and rivals, who have poured resources into trying to dismantle, defuse – or in the case of other jihadi groups, emulate – its online success.
The president said the agreement was not based on trust with Tehran, which he acknowledged is a longtime enemy of the United States, but rather "built on verification".
Belair acknowledged that the "common enemy" doctrine did not permit a public entity to divert water from its natural channel or drainage, and recognized that some post-Albers decisions may have endorsed a rule of strict liability.
