Photos that appeared online over the weekend, depicting Russian army armored vehicles on trains rolling out of the army training base Mulino, 200 miles east of Moscow, are a potentially ominous sign. The Russian army’s newest grouping, the 3rd Army Corps, is on the move–toward eastern Ukraine. The 3rd Army Corps is the first big new formation to take shape as a result of the Kremlin’s urgent initiative, beginning this summer, to recruit new soldiers and stand up new units in order to replace the tens of thousands of troops it has lost in the six months since it widened...