[Sanzig]

American ballistic missiles are all solid fuel, which avoids the need to babysit liquid fuel. For liquid, you either need to keep cryogenic propellant and/or oxidizer constantly topped up, or use a hypergolic fuel (which are almost universally quite nasty). Solid just sits in the silo until you push the doomsday button. Falcon is a liquid fueled rocket with a cryogenic oxidizer (liquid oxygen), so it'd make for a poor ICBM.

[hollerith]

In fact, the US miltary doesn't have any liquid-fueled rocket engines of any type unless perhaps you count the very small engines that refine the trajectory of a MIRV bus after the end of the boost phase of an ICBM or SLBM.

And liquid-fueled rockets are all SpaceX knows.