When I was in, we had duty days which meant that certain specific tasks that had to be performed on duty days included watches. A watch was at a specific place for normally 4 hours at a time. A watch meant you made certain anyone entering your area of watch was authorized and not unauthorized. If your watch post was a building, no one entered the building or the area without proper paperwork and if you did not challenge properly you could very well find yourself in a minor fecal matter storm and with an OOD reprimand in your record.

Duty meant crap work details that were done in addition to your watch assignments. Duty tasks generally took a couple of hours at the most.

Watch posts were armed posts. Duty work was almost always unarmed.

Watch posts on a ship were almost exclusively quarterdeck and OOD in port only. OOD at sea was unarmed and there was no quarterdeck watch.

Certain tasks done with certain equipment were required by Navy regs to have at least one armed escort regardless of at sea or in port and without regard to time of day.

I was on barracks watch one night with a 1903 Springfield (no ammo present) and I was really sick. I passed out and lay there unconscious until my hourly report was missed at which point the OOD showed up and kicked and stomped me until he figured out I was unconscious and not sleeping. At that point he called an ambulance and I woke up the next day in the hospital where I spent the next week.

Oddly perhaps, the most critically secure places I worked in 4 years had elderly (like 80 yo) civilian security guards who wouldn't have made a competent mall cop. They had absolutely zero idea of what was important and who might have access much less what anything important consisted of. Had someone come through the gates with a gun they would have had a couple of heart attacks and the bad guys would have had free reign because there were no other guns accessible legally.

While I was in school, headquarters desk watch consisted of two guys armed with 1911s and an OOD also armed. Sole options for that watch after hours were to take any calls from the front gate or any of the building watch posts and if necessary start waking up command staff. Something I do not recall happening to anyone in a year. But, we had guns and bullets just in case.