On Friday, the presidents of Russia and Belarus met in Minsk and signed new security agreements. After the ceremony, Belarusian President Alexander Lukashenko had a bold question for Russian President Vladimir Putin: Could Belarus get access to Russia’s newest and most powerful Oreshnik missiles?

Putin’s answer? Yes—but not just yet. These cutting-edge missiles, capable of traveling at hypersonic speeds of up to Mach 10 (that’s ten times the speed of sound!), will only be ready for deplo...