Operation Undertone, also known as the Saar-Palatinate Offensive, was a large assault by the U.S. Seventh, Third, and French First Armies of the Sixth and Twelfth Army Groups as part of the Allied invasion of Germany in March 1945 during World War II.
A force of three corps was to attack abreast from Saarbrücken, Germany, along a 75-kilometre (47 mi) sector to a point southeast of Hagenau, France. A narrow strip along the Rhine leading to the extreme northeastern corner of Alsace at Lauterbourg was to be cleared by a division of the French First Army under operational control of the Seventh Army. The Seventh Army's main effort was to be made in the center up the Kaiserslautern corridor.
In approving the plan, Supreme Allied Commander General Dwight D. Eisenhower asserted that the objective was not only to clear the Saar-Palatinate but to establish bridgeheads with forces of the Sixth Army Group over the Rhine between Mainz and Mannheim. The U.S. Third Army of the Twelfth Army Group was to be limited to diversionary attacks across the Moselle to protect the Sixth Army Group's left flank.
Opposing commanders were U.S. General Jacob L. Devers, commanding U.S. Sixth Army Group, and German SS General Paul Hausser, commanding German Army Group G.
Significantly assisted by operations of the Third Army that overran German lines of communication, Operation Undertone cleared Wehrmacht defenses and pushed to the Rhine in the area of Karlsruhe within 10 days. General Devers' victory—along with a rapid advance by the U.S. Third Army—completed the advance of Allied armies to the west bank of the Rhine along its entire length within Germany.
The bulk of the text in this article is taken directly from The Last Offensive, a work of the U.S. Army that is in the public domain. The material was extracted from Chapter XII, "The Saar-Palatinate", pp. 236–265.
Plan
Anticipating early completion of operations to clear the west bank of the Rhine north of the Moselle, Supreme Allied Commander General Dwight D. Eisenhower on 13 February 1945 had told his two American army group commanders—Generals Omar Bradley and Jacob L. Devers—to begin planning for a joint drive to sweep the Saar-Palatinate. Assigned a target date of 15 March, the offensive was to begin only after the 21st Army Group had reached the Rhine. It was to be designed both to draw enemy units from the north and to provide an alternate line of attack across the Rhine should the principal Allied drive in the north fail. The main effort, SHAEF planners contemplated, was to be made by the Sixth Army Group's Seventh Army, which was to be augmented by transferring one armored and three infantry divisions from the U.S. Third Army.
During the first week of March, Devers at Sixth Army Group approved a plan (Operation UNDERTONE) prepared by General Alexander Patch′s Seventh Army. A force of three corps was to attack abreast from Saarbrücken along a 75-kilometre (47 mi) sector to a point southeast of Hagenau. A narrow strip along the Rhine leading to the extreme northeastern corner of Alsace at Lauterbourg was to be cleared by a division of the French First Army under operational control of the Seventh Army. The Seventh Army's main effort was to be made in the center up the Kaiserslautern corridor.
In approving the plan, Eisenhower asserted that the objective was not only to clear the Saar-Palatinate but to establish bridgeheads with forces of the Sixth Army Group over the Rhine between Mainz and Mannheim. The U.S. Third Army of the 12th Army Group was to be limited to diversionary attacks across the Moselle to protect the Sixth Army Group's left flank.
Eisenhower approved on 8 March, the same day that General George S. Patton obtained approval from General Bradley for the plan prepared by the Third Army staff for a major attack across the Moselle.
The 12th Army Group commander in turn promoted the plan with Eisenhower. Noting that the Germans had given no indication of withdrawing from the Siegfried Line in front of the Seventh Army and that Patch thus might be in for a long, costly campaign, Bradley suggested that the Third Army jump the Moselle near Koblenz, sweep south along the west bank of the Rhine to cut the enemy's supply lines, and at the same time press from its previously established Saar-Moselle bridgehead near Trier to come at the Siegfried Line fortifications from the rear. Eisenhower approved the plan without qualification.
Although Devers was briefly reluctant to endorse Third Army operations south of the Moselle lest the two forces become entangled with their converging thrusts, he too in the end approved the plan. He and Bradley agreed on a new boundary that afforded the Third Army a good road leading northeast from Saarlautern to headwaters of the Nahe River, some 56 km (35 mi) northeast of Saarlautern, thence along the valley of the Nahe to the Rhine at Bingen. This boundary gave the Third Army responsibility for clearing the northwestern third of the Saar-Palatinate. Bradley and Devers also authorized the commanders of the two armies—Third and Seventh—to deal directly with each other rather than through their respective army group headquarters.
Facing the undented fortifications of the Siegfried Line, the Seventh Army commander planned a set-piece attack, preceded by an extensive program of aerial bombardment. Before the attack could begin, supplies had to be accumulated, division and corps boundaries adjusted, some units shuffled, and new divisions joining the army fed into jump-off positions. This meant to Patch that the Seventh Army could not attack before the target date, 15 March.
Assault
All along the Moselle, from Koblenz to Trier, the German 7. Armee on 17 March was in peril, if not from direct attack, then from the flanking thrust against the right wing of the 1. Armee by General Walton Walker′s XX Corps. Collapse of the 7. Armee clearly was but a question of time. Soon the German 1. Armee, too, would be in dire straits, for the U.S. Seventh Army two days earlier, on 15 March, had launched a drive against General Hermann Foertsch′s army along a 110 km (68 mi) front from the vicinity of Saarlautern southeastward to the Rhine. Even if that offensive failed to penetrate the Siegfried Line, it might tie the 1. Armee troops to the fortifications while Patton's forces took them from the rear.
The Seventh Army numbered among its ranks several relatively inexperienced units but retained a flavoring of long-term veterans. The VI Corps (Maj. Gen. Edward H. Brooks), for example, and three divisions—the 3rd, 36th, and 45th—had fought at length in the Mediterranean theater, including the Anzio beachhead. The XV Corps (Maj. Gen. Wade H. Haislip) had joined the Seventh Army after fighting across France with the Third Army. A third corps, the XXI (Maj. Gen. Frank W. Milburn), was relatively new, having joined the army in January.
As the Seventh Army offensive began, the basic question was how stubbornly the Germans would defend before falling back on the Siegfried Line. Only Milburn's XXI Corps—on the Seventh Army's left wing, near Saarbrücken—was fairly close to the Siegfried Line, while other units were as much as 32 km (20 mi) away. Making the army's main effort in the center, Haislip's XV Corps faced what looked like a particularly troublesome obstacle in the town of Bitche. Surrounded by fortresses of the French Maginot Line, Bitche had been taken from the Germans in December after a hard struggle, only to be relinquished in the withdrawal forced by the German counteroffensive. On the army's right wing, Brooks's VI Corps—farthest of all from the Siegfried Line—first had to get across the Moder River, and one of Brooks's divisions faced the added difficulty of attacking astride the rugged Lower Vosges Mountains.
Two German corps and part of a third were in the path of the impending American drive. At Saarbrücken, the left wing of General Knieß′ LXXXV Korps would receive a glancing blow from Milburn's XXI Corps. Having recently given up the 559. Volksgrenadierdivision to the 7. Armee, Knieß had only two divisions, one of which was tied down holding Siegfried Line positions northwest of Saarbrücken. Southeast of the town, with boundaries roughly coterminous with those of Haislip's XV Corps, stood the XIII SS Korps (SS-Gruppenführer und Generalleutnant der Waffen-SS Max Simon) with three divisions. Extending the line to the Rhine was the XC Korps (General der Infanterie Erich Petersen) with two volksgrenadier divisions and remnants of an infantry training division.
Although the Germans worried most about a breakthrough in the sector of Petersen's XC Korps into the Wissembourg Gap rather than through Simon's XIII SS Korps into the Kaiserslautern corridor, the shifts and countershifts made in preceding weeks to salvage reinforcements for the 7. Armee actually had left the XIII SS Korps the stronger. In addition to two Volksgrenadier divisions, Simon's corps had the 17th SS Panzergrenadierdivision, at this point not much more than a proud name, but a unit possessing considerably more tanks and other armored vehicles than were to be found in the entire adjacent corps. The American main effort thus aimed at the stronger German units, though at this stage of the war strength in regard to German divisions was but a relative term.
As Patch's Seventh Army attacked before daylight on 15 March, the apparent answer on German intentions was quick to come. Only in two places could the resistance be called determined. One was on the left wing, where the 63rd Infantry Division (Maj. Gen. Louis E. Hibbs) sought to bypass Saarbrücken on the east and cut German escape routes from the city. The fact that the 63rd Division early hit the Siegfried Line provided ready explanation for the stanch opposition there. The other was on the extreme right wing where an attached 3rd Algerian Infantry Division (3e Division d'Infanterie d'Algerie) was to clear the expanse of flatland between Hagenau and the Rhine. There an urban area closely backing the Moder River defensive line and flat ground affording superb fields of fire for dug-in automatic weapons accounted in large measure for the more difficult fighting.
Elsewhere, local engagements sometimes were vicious and costly but usually were short-lived. Anti-personnel and anti-tank mines abounded. German artillery fire seldom was more than moderate and in most cases could better be classified as light or sporadic. That was attributable in part to a campaign of interdiction for several days preceding the attack by planes of the XII Tactical Air Command (Brig. Gen. Glenn O. Barcus) and by D-day strikes by both the fighter-bombers and the mediums and heavies of the 8th Air Force. The latter hit Siegfried Line fortifications and industrial targets in cities such as Zweibrücken and Kaiserslautern. The weather was clear, enabling the aircraft to strike at a variety of targets, limited only by range and bomb-carrying capacity. Among the German casualties were the operations officers of two of the three XC Korps divisions.
Of the units of the outsized (six divisions) XV Corps, only a regiment of the 45th Infantry Division (Maj. Gen. Robert T. Frederick) faced a water obstacle at the start. That regiment had to cross the Blies River at a site upstream from where the Blies turns northeast to meander up the Kaiserslautern corridor. Yet even before dawn men of the regiment had penetrated the enemy's main line of defense beyond the river. Aided by searchlights, they bypassed strongpoints, leaving them for reserves to take out later. As night came, the 45th Division had driven almost 5 km (3.1 mi) beyond the Blies to match a rate of advance that was general everywhere except in the pillbox belt near Saarbrücken and on the flatlands near the Rhine.
On the right wing of the XV Corps, men of the 100th Infantry Division (Maj. Gen. Withers A. Burress) drove quickly to the outskirts of the fortress town of Bitche. Perhaps aided by the fact that they had done the same job before in December, they gained dominating positions on the fortified hills around the town, leaving no doubt that they would clear the entire objective in short order the next day, 16 March.
The only counterattack to cause appreciable concern hit a battalion of the 3rd Division′s 7th Infantry. Veterans of combat from the North African campaign onward, the regiments of the 3rd Division (Maj. Gen. John W. O'Daniel) were making the main effort in the center of the XV Corps in the direction of Zweibrücken and the Kaiserslautern corridor. Although a company of supporting tanks ran into a dense minefield, disabling four tanks and stopping the others, a battalion of the 7th Infantry fought its way into the village of Uttweiler, just across the German frontier. Then an infantry battalion from the 17. SS Panzergrenadierdivision, supported by nine assault guns, struck back. The Germans quickly isolated the American infantrymen but could not force them from the village. Supported by a platoon of tank destroyers and the regimental antitank company organized as a bazooka brigade, another of the 7th Infantry's battalions counterattacked. The men knocked out four multiple-barrel 20 mm (0.79 in) FlaKwagens and seven assault guns and freed the besieged battalion.