The "rods from God" idea was a bundle of telephone-pole-size (20 feet long, 1 foot in diameter) tungsten rods, dropped from orbit, reaching a speed of up to 10 times the speed of sound.
If you actually do the simulation and physics, these claims of supersonic freefall don't hold up. In fact, the Earths atmosphere creates increasing drag on an object in freefall from orbit and orbit velocity such that by the time it reaches the ground it has been slowed (as well as ablated) to barely a few hundred miles an hour. Enough to do serious damage, to a person or home or structure, but nothing like a bomb taking out city blocks.
As I have pointed out on other threads of this topic, if the physics allowed what the articles claim, then we would be getting serious damage routinely from meteors. As it is, most meteors don't even make it to the ground, and its been a very long time since a meteor did any major damage. Earths atmosphere prevents it.
i imagine the mach 10 speed is to deliver them quickly to the target while in orbit then afterward to rod will slow to almost terminal velocity before striking.
or not...
:)