In the west supply problems began slowing down Allied operations, even though the opening of the port of Antwerp in late November improved the situation. The positions of the Allied armies stretched from southern France all the way north to the Netherlands. The Germans wanted to attack the thin line of Allied forces. They thought this would stop Allied advances on the Western Front.
Several plans for major Western attacks were prepared. A first plan was for an attack on the U.S. forces around Aachen, to encircle the U.S. Ninth Army. A second plan was for a "blitzkrieg" attack through the weakly defended Ardennes Mountains. This aimed at splitting the armies along the U.S.—British lines and capturing Antwerp.
Hitler chose the second plan. He liked the idea of splitting the Anglo-American armies. There were many disputes between Montgomery and Patton. Hitler hoped he could make use of these disagreements. If the attack captured Antwerp, four complete armies would be trapped without supplies behind German lines.
Both plans aimed at on attacks against the American forces. Hitler believed the Americans were not able to fight well. He thought that the American people would lose hope upon hearing of an American loss.
"Generalfeldmarschall" (Field Marshal) Walther Model and Field Marshal Gerd von Rundstedt were ordered to lead the attacks.
Model and von Rundstedt both believed aiming for Antwerp was too difficult, given Germany's lack of resources in late 1944. At the same time they felt that being just defensive would only delay defeat. They developed plans that did not aim to cross the Meuse River; Model's being "Unternehmen Herbstnebel" (Operation Autumn Mist) and von Rundstedt's "Fall Martin" ("Plan Martin").
The two field marshals showed their plans to Hitler, who rejected them in favor of his "big solution".
The phrase "Battle of the Bulge" was made up by contemporary press to describe the way the Allied front line bulged inward on wartime news maps.
After the war ended, the U.S. Army issued the Ardennes-Alsace medal to units that took part in operations in northwest Europe. The medal covered the Ardennes sector where the battle took place and units further south in the Alsace sector.
OKW decided by mid-September, on Hitler's orders, that the attack would be started in the Ardennes, as was done in 1940. Many German generals objected, but the attack was planned and carried out. In 1940 German forces had passed through the Ardennes in three days before attacking the enemy, but the 1944 plan called for battle in the forest. The main forces were to advance westward to the Meuse River, then turn northwest for Antwerp and Brussels.
The thick forests of the Ardennes would make movement difficult. There was open ground beyond the Meuse where the Germans could move quickly to the coast.
Four armies were selected for the operation. First was the Sixth Panzer Army, under SS General Sepp Dietrich—newly created on 26 October 1944, it used the most senior and the most experienced "Waffen-SS": the 1st SS Panzer Division "Leibstandarte Adolf Hitler" as well as the 12th SS Panzer Division "Hitlerjugend". The 6th Panzer Army was the northernmost attack force. It was ordered to capture Antwerp.
The Fifth Panzer Army under General Hasso von Manteuffel was ordered to capture Brussels.
The Seventh Army, under General Erich Brandenberger, was ordered to the southernmost attack. This Army was made up of only four infantry divisions, with no armoured groups. As a result, they made little progress throughout the battle.
Also participating in a secondary role was the Fifteenth Army, under General Gustav-Adolf von Zangen. It was located on the far north of the Ardennes battlefield. It was ordered to hold U.S. forces in place. It could also attack if conditions were right.
For the attack to be successful, four elements were needed: the attack had to be a complete surprise; the weather conditions had to be poor to stop Allied air superiority; the progress had to be rapid. Allied fuel supplies would have to be captured because the Wehrmacht was short on fuel. The General Staff estimated they only had enough fuel to cover one-third to one-half of the ground to Antwerp.
The plan originally called for just under 45 divisions, including a dozen panzer and panzergrenadier divisions forming the armored spearhead and various infantry units to form a defensive line. By this time, however, the German Army suffered from a manpower shortage and the force had been reduced to around 30 divisions.
Although it retained most of its armor, there were not enough infantry units because of the defensive needs in the East. These 30 newly rebuilt divisions used some of the last reserves of the German Army. Among them were "Volksgrenadier" units formed from a mix of veterans and recruits formerly regarded as too young or too old to fight. Training time, equipment and supplies were inadequate during the preparations. German fuel supplies were inadequate. Materials and supplies that could not be transported by rail had to be horse-drawn to conserve fuel. The mechanized and panzer divisions would depend heavily on captured fuel. As a result, the start of the attack was delayed from 27 November to 16 December.
Before the offensive the Allies were not aware of German troop movement. During the liberation of France, the French resistance had provided information about German movements. Once they reached the German border, this information was not available. In France, orders had been relayed within the German army using radio messages coded by the Enigma machine. These could be picked up and decoded by Allied code-breakers at Bletchley Park, to give the intelligence known as ULTRA.
In Germany such orders were typically transmitted using telephone and teleprinter, and a special radio silence order was made on all communications about the attack. The major crackdown in the "Wehrmacht" after the 20 July plot to kill Hitler resulted in much tighter security and fewer information leaks. The foggy autumn weather also prevented Allied reconnaissance aircraft from seeing the Germans on the ground.
German units in the area were given charcoal instead of wood for cooking fires to cut down on smoke and reduce chances of Allied observers realizing a troop build up was underway.
Allied High Command considered the Ardennes a quiet sector. Allied intelligence services said that the Germans were unable to launch any major attacks this late in the war. The Allies thought that the Germans were getting ready for defence. The Allies thought that a new defensive army was being formed around Düsseldorf in the northern Rhine. The Germans tricked the Allies by increasing the number of flak batteries in the area and making more radio transmissions in the area.
The attack, when it came, completely surprised the Allied forces. The U.S. Third Army intelligence chief, Colonel Oscar Koch, the U.S. First Army intelligence chief and the SHAEF intelligence officer had warned that the Germans might attack the U.S. VIII Corps area. These warnings were ignored by the U.S. 12th Army Group.
Because the Ardennes was considered a quiet sector, the Allies used it as a training ground for new units and a rest area. The U.S. units deployed in the Ardennes thus were a mixture of inexperienced troops (such as the U.S. 99th and 106th "Golden Lions" Divisions), and veteran troops sent to that sector to rest (the 28th Infantry Division).
Two major special operations were planned for the attack. By October it was decided that Otto Skorzeny, the German commando was to lead a task force of English-speaking German soldiers. These soldiers were to be dressed in American and British uniforms. They would go behind American lines and change signposts, misdirect traffic, cause disruption and seize bridges across the Meuse River between Liège and Namur.