The theory is correct, reality is that they are "expected" to respond to any security incident on the aircraft that represents a threat to aircraft,crew, or passengers. They brief with us on board prior to pax boarding..some are on board early, others come aboard with pax...we have several on the 400, some flights more than others dpending on destination and related issues.
The weapons piece only comes into play in very specific circumstances..they do have other options available besides guns depending on circumstance.
Hopefully they are awake and cognisant when needed...not always the case in the past unfortunately.
Thankfully we CAN rely on our ABP's who have very little tolerance for anyone behaving in a way that threatens their safety. The troublemaker in some past cases has left the aircraft in a body bag.
MS