Ok, I'm a guy. I like things that go "bang!" The bigger, the better. So pardon me while I savor the thought of the Air Force testing a new 21,000 pound bomb. No, that's not a typo... 21,000 pounds.

It appears to be a development of the old 15,000 pound BLU-82 "daisy cutter", which was originally developed during Vietnam to (VERY QUICKLY) clear chunks of jungle for helicopter landings. Having made more than they could use, the -82 ended up being a bomb in search of a mission. See, the -82 isn't really a general purpose weapon.

In spite of its massive size, these kinds of weapons really aren't capable of the same kind of damage that, say, a general purpose (GP) or cluster bomb (CB) is. The GP bomb does much of its damage via the fragmentation of its casing, while the CB uses a variety of methods including fragmentation and "shaped charges".

The -82 and (presumably) this new device works via raw "overpressure". Imaging sticking a pin in a filled balloon very close to your face... the "POW!" you feel when it pops is overpressure. Now, this can be nasty, especially if a lot of flying debris is involved. However, as long as you're in an enclosure that can withstand this pressure (i.e. a tank, a bunker, an APC) you'll be deaf, but you won't be dead.

In spite of what the radical lefties and protestors like to shriek about, a bomb that can't take out military targets isn't much use to the armed forces. So the -82 was warehoused and other more potentially potent designs were shelved. At first, their use in the gulf war was at least as much about freeing up warehouse space (each -82 is about 5x5x5 feet in size) as it was about any real tactical use.

However, it was discovered this massive overpressure was extremely useful for setting off mines. Roll one of these things out the back of a C-130 (it's too damned big and heavy to fit in anything else) and huge paths could be blown through minefields in seconds. Since most tinpot third-world armies treat mines like grass seed, suddenly the monster had a purpose again. They also used them in Afghanistan to close up cave entrances and trigger landslides.

More overpressure = more dead mines, so in this case bigger is most definitely better. I have a feeling the introduction of the C-17, which can haul more stuff than the much older C-130 but fit on the same airfields, had an influence.

Again, want to emphasize that this is not a monstrous general-purpose weapon. It is not for use on civilian areas, or as a way to kill more people faster. It is an extremely specialized system designed to be used in very specific situations. Any protestor who tells you differently is either stupid, ignorant, or pushing an agenda.

Update: Found this picture of a BLU-82 on the FARK comments. Ok, so it's quite a bit bigger than 5x5x5. Never was any damned good at measurements.