Green’s Dictionary of Slang

armed for bear phr.

[hunting jargon, the killing of bears requires a large weapon]

very heavily armed, lit. and fig. (cf. loaded for bear under loaded adj.).

[US]C. Himes Cotton Comes to Harlem (1967) 15: The driver hesitated a moment longer. ‘They’re armed for bear.’.
P.T. Deuterman Scorpion in the Sea 235: Linc is going to come up to CIC armed for bear. He’s gonna try to persuade you that they had something, and he’s gonna be pissed off that we broke it off.
British Pacific Off Road Equipment [Internet] Lock the center differential, engage both Air Lockers, and THEN you’re armed for bear!
Creative Loafing (Atlanta GA) 9 Oct. [Internet] [headline] Armed for Bear. Atlanta cop takes down unleashed Labrador.