describes a fictional phase of crystalline frozen water (Ice-9) that melts at high temperatures and has the property of converting any liquid water it comes into contact with into more Ice-9.

It is developed by the Army so that its solid form can be sprinkled on mud or slushy, melting snow causing it to harden instantly so it can support heavy vehicles. The only problem is that if even one crystal of the stuff falls into the sea it would cause the entire ocean, top to bottom, to freeze instantly into a room temperature solid.

I suppose its a metaphor for nuclear weapons--a scientific development that allows you to win a war, but can destroy human civilization in an instant.