I don't want to address today's tragic events at Fort Hood directly; I have no first- or second-hand knowledge about the incident. But I would liek to address some of the misconceptions many Kossacks seem to have about servicemembers, military bases, and life thereon. Many people seem to have a distorted view of the military and people who serve in it.
1. They're not all highly trained for combat.
Now, today's shooting happened on an Army base, so it's pretty safe to say that all the soldiers in the area had some training as riflemen in Basic. If a similar incident had occurred on a Navy base, it wouldn't even be possible to say that much; Navy firearms training consists of a single morning's lecture and an hour of shooting a 9mm pistol and a fake laser-targeted shotgun. The Army gets significantly more than that - they pack their rifles around with them for quite some time in the field, and they have to qualify regularly on the rifle range, and they get some minimal unarmed combat training. But very few are highly trained. Most go on, after a couple of months at Basic, to learn some pretty ordinary skilled trade or profession - to fix diesel engines, or to work in a logistics department, or to translate a language.
2. They're not all young and fit.
The Army would certainly like us to believe that they are. But the truth is that in an average place on base, you're likely to find that some significant fraction of the population consists of aging, somewhat paunchy, balding, possibly sick and definitely exhausted older men. Another fraction is likely to be pregnant women, retired or veteran or civilian employees of all shapes and sizes, and injured or disabled servicemembers. This is particularly true at a non-deploying unit where the work is largely desk work; many civilians are often hired to work in these places, and the servicemembers who work there are often either older men and women getting ready to retire or young people assigned there while they are pregnant or recovering from an injury.
3. They're not all primed to react assertively to violence.
People who serve in the military, when they're at "home" in a relatively comfortable environment where they feel safe, tend to react to violence or danger in much the same way that civilians do. They're frightened by it, they don't immediately know what to do, they react instinctively, they may run or cower in a corner or freeze or dive for cover, but very few if any will have the presence of mind to act 'heroically.' That part of the brain can't be turned on constantly. A constant state of 'alert,' of being on edge, of being primed to react is not healthy. In fact, it's one of the symptoms of PTSD. Most servicemembers don't have PTSD, and most are able to switch off the 'alert' system outside of real combat or drills designed to trigger it. This is what allows them to go about their daily lives normally. it's also what allows them to be victims of a crime, just like the rest of us.
4. They don't carry weapons on base.
This is a safety issue. There are actually very few guns on base not locked up in an armory, and all of the legal ones are in the possession (and positive control) of a military police officer or other authorized armed security detail in the line of duty. In theory, this policy is intended to prevent tragedies like this. In practice, it works very well most of the time, but unfortunately it's impossible to enforce it perfectly against a shooter who evidently did not value his own life or career.