The phrase "man army" refers to a large group of men gathered together. It implies a sizable force of men, either for a specific purpose or to depict a strong group of people. Full definition
You're a one man army space pilot up against an entire facility of robot ships. (escapistmagazine.com)
There's just no sense of danger when you're facing off against human enemies because you feel like a one - man army capable of blazing through hundreds of them. (wolfsgamingblog.com)
With this setup you'd probably expect your typical one - man army on a rescue mission action game storyline. (gamerstemple.com)