"Pardon my ignorance, but can anyone tell me what happens on impact with a concrete bomb? They don't explode, so what do they do? Just shatter like a big rock?"
Honestly, not much... a 500 pounder is about 16" in diameter and a 2000 pounder is about 24" diam (my guess from eyeballing them on a preflight). If it hits dirt at a high impact angle it will bore a 16" to 24" hole for a loooong way down into the earth. I have heard stories of inerts (concrete filled bombs) going over a 100' down into non-rocky dirt. However, if it hits concrete or a vehicle it can cause a small pattern of shrapnel as its passing through (converting vertical velocity into horizontal velocity imparted to the fragments). You basically have to hit what you are trying to kill. If its a person, you would have to physically touch him with the bomb as it went by. Most of the time they are dropped from miles away, so trying to hit something as small as a person is more a matter of luck. A vehicle is easier obviously. Now if the bomb hits at an angle (versus straight down) it can "broach", which means it penetrates a few feet into the dirt and then skips back up through the dirt and starts tumbling and bouncing through the air and off the ground for MILES!!!!! I've done it and seen it, and its impressive!
Cool.