Explain The Need For 1.6 Billion Rounds Of Ammo For Homeland Security. It's Time For A "National Conversation".

A recent news item making the rounds tells us that the DHS is looking to buy 1.6 billion rounds of ammunition.

If only .1% of these bullets makes its way into a person, that's still well over the number of people living in 13 US States.

Please explain why the DHS needs so much ammunition?