The low-flying, subsonic Neptune lends itself to the land-attack role, just like its predecessor missiles—the Kh-35 and Harpoon—do. To give the first-generation, anti-ship-only Harpoon a land-attack mode in its Block II model in the late 1990s, American missile-maker Boeing added GPS-aided inertial navigation, complementing the original Harpoon’s radar seeker. The Ukrainian navy reportedly used some of its Neptune anti-ship missiles in the missiles’ secondary land-attack mode to blow up a Russian air force S-400 air-defense battery in western Crimea on Wednesday. That the one-ton Neptune can strike targets on the ground should come as no surprise. Ukraine’s Luch Design Bureau...