After some early hesitation over concerns the systems could be used by Ukrainian forces against Russian territory, reluctantly drawing the U.S. into the fight, Washington said it would initially send four Himars to Ukraine, and train Ukrainian forces to use them. These advanced systems are mobile launchers capable of striking targets from a maximum distance ranging from about 60 kilometers to nearly 500 kilometers depending on the type of ammunition used. “We needed to persuade them, to show them proof,” said Mr. Reznikov. “In the Izyum case, we were precise [in targeting] a Russian command center for aerial operations. It...