In a fierce battle lasting ten days, the American and German lines were often confused. During the first three days, the battle raged in and around Rocherath-Krinkelt. Attacking Elsenborn Ridge itself, the Germans employed effective combined arms tactics and penetrated the American lines several times, but their attacks were not well coordinated and were frustrated by the rugged terrain and the built-up area. To push the Germans back, the U.S. Army called in indirect fire on their own positions, and at one point rushed clerks and headquarters personnel to reinforce their lines. The Americans had positioned considerable artillery behind Elsenborn Ridge and these artillery batteries repeatedly pounded the German advance. The Germans, although possessing superior armor and numbers, were held in check by the Americans' well-prepared and defensive positions, new proximity fuses for artillery shells, and innovative tactics, which included coordinated time on target artillery strikes.