The phrase "army from which" is correct and usable in written English.
It can be used when referring to a specific army that is the source or origin of something, often in a comparative or descriptive context.
Example: "The general spoke of the army from which he had drawn his most trusted advisors."
Alternatives: "army that" or "army of which".
He may look like a reformer, but he owes his job to the army from which he hails.
It had become obvious, however, that he could no longer remain in the army, from which he resigned in 1831.
But his voice intensified with grievance when the subject turned to his short-circuited career in the Army, from which he was discharged in August involuntarily.
Of course, seeing their sons disappear into an army from which they may never return, is not popular with their families.
His uncle, Jacques-Marie, served the Bourbons and the July Monarchy, which ruled France in 1830 48, and helped Cavaignac regain his appointment in the army, from which he had been dismissed in 1831 because of his republicanism.
As a youngster he joined gangs of other kids who stole from stores, stole cars for joy-rides In 1945, at the age of 18, he joined the Army, from which he received a dishonorable discharge because of insubordination.
On Friday opposition forces claimed to have captured a major army checkpoint from which it controlled one of the main roads into the city centre.
Pressured by the international blockade, Serbia withdrew its army from Scutari, which was subsequently occupied by a joint Allied ground force.
When he produced a Catholic heir, the tension exploded, and leading nobles called on his Protestant son-in-law and nephew, William of Orange, to land an invasion army from the Netherlands, which he did.
Weihui is the daughter of an army officer and spent three years of her childhood living in an army-occupied temple from which the monks had been expelled during the chaotic Cultural Revolution.
According to this letter, Sargon, in 714, led the Assyrian armies from Kalakh, which at the time was still his residence, into the areas around modern As-Sulaimānīyah in Iraqi Kurdistan and into the highlands of the Zagros range beyond.
