<P> The surprise attack caught the Allied forces completely off guard . American forces bore the brunt of the attack and incurred their highest casualties of any operation during the war . The battle also severely depleted Germany's armored forces, and they were largely unable to replace them . German personnel and, later, Luftwaffe aircraft (in the concluding stages of the engagement) also sustained heavy losses . </P> <P> The Germans officially referred to the offensive as Unternehmen Wacht am Rhein ("Operation Watch on the Rhine"), while the Allies designated it the Ardennes Counteroffensive . The phrase "Battle of the Bulge" was coined by contemporary press to describe the bulge in German front lines on wartime news maps, and it became the most widely used name for the battle . The offensive was planned by the German forces with utmost secrecy, with minimal radio traffic and movements of troops and equipment under cover of darkness . Intercepted German communications indicating a substantial German offensive preparation were not acted upon by the Allies . </P> <P> The Germans achieved total surprise on the morning of 16 December 1944, due to a combination of Allied overconfidence, preoccupation with Allied offensive plans, and poor aerial reconnaissance . The Germans attacked a weakly defended section of the Allied line, taking advantage of heavily overcast weather conditions that grounded the Allies' overwhelmingly superior air forces . Fierce resistance on the northern shoulder of the offensive, around Elsenborn Ridge, and in the south, around Bastogne, blocked German access to key roads to the northwest and west that they counted on for success . Columns of armor and infantry that were supposed to advance along parallel routes found themselves on the same roads . This, and terrain that favored the defenders, threw the German advance behind schedule and allowed the Allies to reinforce the thinly placed troops . Improved weather conditions permitted air attacks on German forces and supply lines, which sealed the failure of the offensive . In the wake of the defeat, many experienced German units were left severely depleted of men and equipment, as survivors retreated to the defenses of the Siegfried Line . </P> <P> The Germans' initial attack involved 410,000 men; just over 1,400 tanks, tank destroyers, and assault guns; 2,600 artillery pieces; 1,600 anti-tank guns; and over 1,000 combat aircraft, as well as large numbers of other AFVs . These were reinforced a couple of weeks later, bringing the offensive's total strength to around 450,000 troops, and 1,500 tanks and assault guns . Between 63,222 and 125,000 of their men were killed, missing, or wounded in action . For the Americans, out of 610,000 troops involved in the battle, 89,000 were casualties . While some sources report that up to 19,000 were killed, Eisenhower's personnel chief put the number at about 8,600 . British historian Antony Beevor reports the number killed as 8,407 . It was the largest and bloodiest battle fought by the United States in World War II . </P>

How were allied troops able to defeat the german advance at the battle of the bulge
find me the text answering this question