Mostly mentioned for its exactions on the Ardennes ground, the gepanzerte Kampfgruppe « Peiper « remains even today the object of all the questioning as for its implication during the battles of Stavelot and La Gleize, as well as the involvement of its Tiger II in front of American armored units. While the unit has crews of exception, counting in its ranks most of the symbolic Panzerwaffe’s Aces, that it benefits from the effect of surprise, the schwere SS-Panzer-Abteilung 501 suffers a resounding defeat during the battle of the Bulge. How a vehicle was judged among the most powerful of the conflict, was able to undergo about hundred percent of losses? A posteriori, can we speak about a tactical failure? This study, led by a duet of ardennes authors worn-out to the questions relative to this episode of World War II, answers the double objective to reconstitute the facts and to explain why, finally, he could not be there differently. Text and captions in French