These terms are used quite often, especially after 9-11.
The "finest" is probably the oldest. Most sources claim that it was coined by police chief George W. Matsell. "Finest" ("best" was also used) probably dates to at least July 1874, when Matsell said, "I intend, sir, to make of this the finest police force in the world." The comedian Gus Williams starred in the play One of the Finest in the early 1880s. I believe that "the finest police in the world" is meant to be a similar phrase to Civil War General Joseph Hooker's "finest army on the planet."
The "bravest" probably dates from the 1890s.
The "strongest" and "boldest" are much newer; the first New York Times citation for "boldest" is in 1996, the first hit for "strongest" is in 1981.