The phrase "a formidable army of" is correct and usable in written English.
It can be used to describe a large and powerful group, often in a military or competitive context.
Example: "The kingdom was defended by a formidable army of skilled warriors, ready to face any threat."
Alternatives: "an impressive force of" or "a powerful contingent of".
He manages to escape and frees other slaves, forming a formidable army of rebels.
Southern Sudan has a formidable army of tens of thousands of soldiers, including many trained by the United States.
In Manchuria, Lin Biao was forging a formidable army of veteran cadres from northern China and natives of Manchuria, now well equipped with Japanese weapons.
Five years later, Ms. Lipstadt, a professor of Modern Jewish and Holocaust Studies at Emory University in Atlanta, won a drawn-out court case along with her publisher, Penguin Books, but only after spending more than $3 million and enlisting a formidable army of experts who had to prove that what she had said about Mr. Irving was true.
This means that every founder we invest in becomes a partner in Kindred, and therefore into a partner in each other's companies, and we can turn a partnership of four into a formidable army of partners, all rewarded for supporting and nurturing each other.
It is being called a war on cancer, but it may be a slight misnomer, because cancer is not one disease; it is a formidable army of many diseases.
The dreary economic fears and worries listed at the top will galvanize the boomers -- "leading edgers" and "trailing edgers" -- to create a formidable army that will change the shape of America just as they have defined American culture at every other stage of their lives.
Forty-thousand strong, the NYPD represents a formidable army: Forty-thousand souls armed, organized, and trained to think of others as either victims or perpetrators.
But when you put enough of them together and under the control of a few people who know what they are doing, they can become a formidable army".
The General Accounting Office recently estimated that 52percentt of the nation's 1.6 million farm workers are here illegally, a formidable army whose presence openly violates American laws.
No matter how solemn the binding oaths of blood brotherhood might be, because steppe horsemen had always followed their own tribal leaders to war, any quarrel among chiefs could immediately dissolve a formidable army into its original warring fragments.
