When a National Guard unit gets sent on a federal mission (to Afghanistan for instance) they are alerted months ahead of time (usually), sometimes at weekend "drill." When a unit gets put on state active duty the alert is usually a phone call, in my case it has always been when I was at work. Some one calls you and tells you that you have a certain number of hours to report to the armory.
Usually there is some event that you are watching closely and hoping that you won't be needed, won't be called. I've been on state active duty for riot control, flood abatement and hurricane relief. Every time when the phone rang I knew exactly what it was.
When I was called up for Katrina there were only a handful of us that had the early call. LTC John (then MAJ John) was already at the armory when I arrived. He had actually been there a day before I had to report, but he didn't go with us on that faithful drive south, into the storm ravaged land.
We would have reported to our home armory on North Avenue and Kedzie Avenue in Chicago, in the corner of Humboldt Park. The armory was built in the 1930s when America had thought they had seen the last of war, thought that National Guard service was all fun and games. It was years before the shock and horror of Pearl Harbor, and a millennium separated from the devastation wrought on our own land on a sunny day in September.
On the sunny day in September which I was to report our armory was closed for some badly needed repairs. Walls and ceilings were being rebuilt, windows replaced, electricity and phone lines run. The things they found, bricked away for decades would be another story. For this one, we reported to the armory at the North Riverside Maintenance Center and Training Site.