I was reading about this on Wikipedia. Soviet physicist Nikolai Fedyakin believed he'd discovered a new state of water that was syrupy and remained liquid at both lower and higher temperatures, and the American military was very concerned with their ability to produce as much of the substance as the Soviets were (though it was later discovered that Fedyakin's methods were flawed, and what he'd taken to be a new state of water was simply ordinary water with pollutants in it).
But why was America so worried about this? Was it simply run-of-the mill Cold War paranoia about the Russians having something we didn't, or were there specific potential military applications of the supposed substance which they believed would grant whichever nation possessed the most of it a specific advantage?
The general idea is that for everything the Soviet Union revealed they had done, the belief was that there were dozens of things that weren't revealed. The idea that the Soviet Union had managed to synthesize a new type of water that the USA couldn't set into motion the same paranoia that fills the Cold War.