“If you want to live, dig.” The words, often spoken by Ukrainian troops, are universal advice for trench warfare in general, but especially for both sides in Russia’s war against Ukraine. Normally expressed as advice to the individual soldier, the maxim now applies to the country as a whole. Twenty-one months into the full-scale war, World War I-style tactics, with the high-tech edge brought by drones and other innovations, continue to dominate. Russia and Ukraine are diving head-long into a winter campaign looking to be no less brutal than the last, and it is Russian forces that have taken th…