Do the Swiss really buy Howitzers and anti-aircraft guns?

I already knew that the Swiss buy and keep firearms very freely, but I just read that, with permits, they can also buy Howitzers, anti-aircraft guns, and other military weapons from their government. (At least, they could in 2001, when this book was published.)
Assuming that's true, why in the world would a private citizen buy a Howitzer or especially an anti-aircraft gun? What can you do with an anti-aircraft gun other than shoot down aircraft? It's not an appropriate hunting weapon, and it's too large to carry for self-defense. The only useful effect of the government offering large military weapons to individuals, that I can see, is that it would be very helpful in discouraging invasion by foreign countries. I know the Nazis left Switzerland alone, and at least one reason is obvious.
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P.S. And this question is coming from an NRA member (though I let my membership lapse) who respects Switzerland as possibly an even freer country than America.