No offense taken and you don't sound like a D***, it's a very intelligent question.... Well... Just because there is a ton of BA stuff there doesn't mean that it isn't easily overrun. I'm just saying that most people have the impression that an army post has a ton of soldiers walking around with tons of ammo. When I was in the army, and was unlucky enough to be put on ammo detail at Ft Irwin, there was no reactionary force and there were only 2 soldiers there with side arms. The rest of the folks who worked at the ammo facility were civilians with out guns. It was pretty much the same on Ft Stewert when I was stationed there. I did get out of the army just before 9-11 so things may have changed, but getting to the ammo is not a simple task. If there are only a couple guys holding weapons, and they would definately be reluctant to shoot especially being stateside. It's unlikely that they would be warned prior to seeing the first zombie.
I definately agree that one could get to the motorpool quickly, jump in an M1 and start crushing zombies.... But how many of the soldiers stationed there can drive a tank, or a Bradly, or an M113 ? The majority of the troops there are support troops who wouldn't know where to even look for the "start" button on an M1 or a Bradley. but the rate of infection and and confusion that must have been happening would be overwheming and would take soldiers by surprise as it did everyone else.
Ultimately, soldiers are people too and would react much in the same way as civilians... they would be disoriented and confused and it would be pretty easy for a bunch of zombies with ever growing number to take over anything. You mentioned that Irwin is really far out. True, but knowing about the zombie outbreak ahead of time I suppose would be the key to wheter or not it would be easy to defend. If they had no warning ahead of time then I would argue that it would be easily overrun.
Running over shi* in an M1 is fun and if it were zombies, that would be even more fun.