(idiomatic, military, of a weapon) Held with two hands as in "port arms", but carried well above the head. The high port is often the position taught for running (at the double) or charging.
(idiomatic, by extension) Sticking up; (of hair, etc) standing up at a marked angle.
(idiomatic, by extension, of anything, not just a weapon) Held in front of the body, especially in an authoritative or aggressive way.
(idiomatic, slang, by extension) At once, quickly; unhesitatingly, vigorously.
(idiomatic) Positioned ready for immediate use.
Source: en.wiktionary.org