As the Supreme Commander of Allied Forces in the European theater, Gen. Dwight D. Eisenhower is remembered as one of the most masterful military figures in history, the man behind the bold and superbly-executed Normandy invasion in June 1944 that led to Nazi Germany’s defeat less than a year later.

But before Eisenhower’s great military successes, there was a great failure. When he first faced the Germans in Tunisia in February 1943, his forces took a brutal beating in the battle of the Kasserine Pass. The battle is regarded by some as the most humiliating U.S. combat setback in World War II, with American forces suffering more than 6,000 casualties.

The loss was so devastating that British allies began to question Americans’ ability to fight. But after figuring out what had gone wrong, Eisenhower made sweeping corrections. He reorganized his forces to work together in a more cohesive fashion, shook up his intelligence operation and brought in the brash, aggressive Gen. George S. Patton to shape up the U.S. Army’s ground combat force in Tunisia.

Just as important, Eisenhower didn’t lose faith in his men. Instead, he was able to see what they did right in the battle, and to build upon those strengths.

“The U.S. Army, the entire Allied force, was restructured from top to bottom after Kasserine,” Robert Citino, the Samuel Zemurray Stone Senior Historian at the National WWII Museum in New Orleans, explains. “If Eisenhower wasn’t ready for Kasserine, he also showed that he knew how to jump start things.”

As the National World War II Museum’s website details, in November 1942 Eisenhower led the American and British forces in Operation Torch, an invasion of Axis-held North Africa. The Allied forces moved eastward, with the British forces under Gen. Bernard Montgomery taking Tripoli in late January. Then the Allies crossed the Atlas mountains, with a plan to head toward the Mediterranean and split the German forces to the north and south.

In response, German Field Marshal Erwin Rommel used two of his tank divisions to push back the Allied line. Then, he saw an opportunity. He decided to launch a direct counterattack against the Allies through the Kasserine Pass, a gap in the mountains in central-western Tunisia.

Early in the morning on February 19, the Germans struck, and over the next week or so, inflicted heavy punishment upon the Allies. The inexperienced II Corps, commanded by Eisenhower subordinate Maj. Gen. Lloyd Fredendall, did particularly badly.

“The American Army looked like all the other armies who fought the Germans for the first time,” Citino says. “The Germans were well-trained and highly experienced, and they caught a green U.S. II Corps.”

To make matters worse, Fredendall had split up elements within divisions and assigned them separate individual tasks, so that they fought in an uncoordinated fashion.

Eventually, in the last few days of the battle, the U.S. forces rallied. By the end, “their line had stiffened, and they were blasting the Germans with concentrated artillery fire,” Citino explains. That halted the German offensive, and Rommel—faced with overextended supply lines and Allied reinforcements rushing into the fray—ordered his forces to return to their starting positions.

While the Germans had been repulsed, the battle had been a costly one. The U.S. forces suffered more than 6,300 casualties, including more than 300 killed. The Germans, in comparison, suffered around 1,000 casualties, including 200 killed, 550 wounded and 250 missing, according to Blumenson.

To add to the pain, the poor U.S. performance earned scorn from the experienced British forces. As Eisenhower biographer Carlo D’Estes details, British soldiers began derisively referring to the Americans as “our Italians,” a reference to the Germans’ lightly-regarded ally.

For Eisenhower, his first battle turned out to be an embarrassing moment. But when Eisenhower reported back to his boss in Washington, U.S. Army Chief of Staff George C. Marshall, he tried to put a positive spin on events. “All of our people, from the very highest to the very lowest, have learned that this is not a child’s game,” he wrote. His forces were ready and eager to get down to business.

As Eisenhower examined what had happened, he saw that despite the shortcomings at the top and his forces’ inadequate training, his enlisted men and field officers were quick learners and tough enough for the job.

“Eisenhower came out of the battle with renewed confidence that he had the men, the firepower, and the equipment he needed, if only that force was better commanded,” Citino explains. “And he could do something about that.”

One of Eisenhower’s key moves was to relieve Fredendall, about whom he’d had misgivings even before the battle, from command of the II Corps. He replaced him with Maj. Gen. George S. Patton, a tough taskmaster and aggressive, daring tactician. Patton turned out to be the perfect man to retrain the II Corps and incorporate the lessons learned from Kasserine Pass.

“Morale in the II Corps was shaken, and the troops had to be picked up quickly,” Eisenhower later wrote in his memoir, Crusade in Europe. “For such a job, Patton had no superior in the Army….[his] buoyant leadership and strict insistence upon discipline rapidly rejuvenated the II Corps and brought it up to fighting pitch.”

“Eisenhower's replacement of Fredendall with Patton shows that Eisenhower was a decisive leader who could make the tough decisions,” Leo Barron, author of Patton’s First Victory: How General George Patton Turned the Tide in North Africa and Defeated the Afrika Corps at El Guettar, says.

“Eisenhower realized after Kasserine Pass that Fredendall had spent most of the battle hunkered down in a command bunker, miles away from the battle while leaving his subordinates leaderless and confused for most of the fighting.”

Eisenhower also overhauled his intelligence operation, which had provided faulty information about the position of German forces. As he later noted in his memoir, “staffs were too prone to take one isolate piece of intelligence in which they implicitly believed, and to shut their eyes to any contrary possibility.”

In addition, Eisenhower set a tougher standard for all of his officers. According to Ambrose, Eisenhower told Patton that he expected him to be “perfectly cold-blooded” about getting rid of anyone whose ability he doubted.

“He adopted a much more ruthless, bottom-line attitude in relation to subordinate commanders,” John C. McManus, a Curators’ Distinguished Professor of U.S. military history at the Missouri University of Science and Technology and author of several books on World War II, says. “While he seldom personally fired them, he made it known that anyone who did not perform was liable to be cashiered.”

Eisenhower instilled in his forces the concept of fighting as one unit, rather than as disjointed pieces. “Before Kasserine Pass, the U.S. Army was a group of regiments strung across the Tunisian desert,” Citino says. “After that, they began to fight as concentrated, unified divisions with combined arms—heavy firepower, armor, and infantry all working together.”

Eisenhower’s new approach quickly bore fruit a month later in the battle of El Guettar, which Barron noted was “the U.S. Army’s first major tactical victory against the Wehrmacht.”

The Allied forces ultimately were victorious in North Africa, and went on to take Sicily and Italy as well. About a year and a half after the near-catastrophe at Kasserine Pass, Citino says, “it’s the same U.S. Army that’s landing in Normandy, and it’s pretty damn good there.

"If there’s one individual responsible for that turnaround more than any other, it’s Eisenhower.”

Watch a preview of the two-night event Presidents at War, premiering Sunday, February 17 at 8/7c.