Well directed kinetic energy can be devastating and has been used for such effect since ages, for example the old canons with passive cannon balls. Rail guns are their new sought after variants.

The famous bunker-busting smart-bombs circa first gulf-war were fin stabilized old tank barrels packed with explosives. It is their weight, owing to the high density metals used in the barrels and their small cross section (and hence extremely high terminal velocity) that gave them their extreme penetrative punch. Enough to pierce through tens of layers of strengthened concrete, each several feet thick and explode with devastating effects underneath. It was very important that they did not topple in flight though. So stabilization was critical.

Even the modern anti-tank weapons are essentially glorified darts, but much, much heavier. They kill tanks by sheer kinetic energy alone. They have been found to be harder to defend against, compared to other variants like HEAT that penetrate tank armor by the use of a high speed, dense jet of liquid metal, or HESH which are sort of like cow-pies made of high explosives that set off spalling bending moments inside the tank 'hull'.

To generate the force of a 1 ton TNT explosion, a shell shaped bomb moving at 800 ft per second will need to weigh 311,000 pounds. [K.E.=1/2 x m x v x v]

It takes a fraction of this to dent a tank out of commission, provided you're accurate. The overpressure wave bouncing around inside the tank cabin created by a direct hit probably has stunning effects on the crew and may not kill them if the cabin isn't crushed - although it could do terrible damage to the ears, lungs and stomach.

I wonder what they're using for guidance. GPS and inertial guidance aren't accurate enough and anyway aren't useful against moving targets.

That leaves laser guidance kits, which tend to be pretty expensive. Probably takes more than one attempt on average, too.

On the other hand, you probably don't need to worry much about temperature and humidity when you store concrete munitions. Or maybe they mix up a batch of bombs before the sortie - "You can't launch yet. The concrete isn't dry."

Pretty sure the US did this during the first gulf war to destroy stationary targets without the pesky explosion.

Shades of Heinlein's "Harsh Mistress" - launching is easy when you're "uphill" from the earth, and rocks are cheap.

I wonder how accurate you have to hit the target to get the intended consequences.

This is brilliant.

Wasn't there a military program for dropping metal rods from space? Does this sound at all familiar to anyone?

This is an awesome idea. Even if the devices miss, they'll create terror in people thinking about the unexploded bombs.

Soon: imaginary bombs, weighting sqrt(-1) t :)