Using so-called "Blitzkrieg" tactics, Guderian, Paul Ludwig Ewald von Kleist and other field commanders such as Rommel broke the hiatus of the Phoney War in a manner almost outside the comprehension of the Allied — and, indeed, the German — High Command. In actual tank-on-tank encounters the German armor performed poorly, but as a coherent unit, the combined arms tactic of the Blitzkrieg shocked the Allies.