Russia is developing some sort of hypersonic warhead for use on its new Sarmat heavy ICBM. This is advertised as an effective countermeasure to American anti-missile interceptors. The Russians are working hard to put the hype back into hypersonic, but it is unclear precisely how this new warhead is expected to evade missile defense interceptors. As best as one can imagine, the vehicle would perform a trans-atmospheric trajectory in which the flight altitude was typically too deep in the atmosphere for exo-atmospheric kill vehicles to conduct an intercept. The hypersonic vehicle would be initially boosted to high speed by an ICBM, and then continue under its own power, skipping along the top of the atmosphere. This concept was first studied by the German engineer Eugene Sanger, whose “Silver Bird” antipodal bomber was intended to bomb New York City. During the early years of the Cold War the Soviet Union investigated a variety of such mixed propulsion configurations, including rocket boosted cruise missiles and rocket launched boost glide vehicles.