Einen schönen Tag allerseits!

The image is chilling, bordering on surreal: On December 18, 1941, as World War II rages and countless innocents endure the horrors of the Third Reich’s “final solution” — killing operations at the Che%u0142mno death camp, for instance, began less than two weeks before — Adolf Hitler presides over a Christmas party in Munich. Stark, jarring swastika armbands offset the glint of ornaments and tinsel dangling from a giant Tannenbaum; festive candles illuminate the scene. Confronted with the image, the question naturally arises: How could Nazi leaders reconcile an ideology of hatred and conquest with the peaceful, joyous spirit of the Christian holiday — much less its celebration of the Jewish-born Christ? Here, LIFE.com presents astonishing photos from this unsettling affair, and the equally remarkable story behind them.

In a shot captured by Hugo Jaeger, one of Hitler’s personal photographers, huge streamers of tinsel hang from the rafters of the Lwenbrukeller beer hall, where SS officers and cadets sit down for a feast. The Nazi Christmas photos published here were part of an enormous stash of color transparencies Jaeger buried in glass jars on the outskirts of Munich in 1945, near the war’s end. Advancing Allied forces had almost discovered the pictures during an earlier search of a a house where Jaeger was staying (a bottle of cognac on top of the transparencies distracted the troops), and Jaeger — justifiably terrified that the photos would serve as evidence of his own ardent Nazism — cached them in the ground. A decade later, he exhumed the pictures; 10 years after that, he sold them to LIFE, which published a handful in 1970. (Other highlights from the Jaeger set were published for the first time by LIFE.com in June 2009.)

As for the religious views of Hitler himself, the evidence is conflicting: In public statements he sometimes praised Christianity (once calling it “the foundation of our national morality”), but in private conversations — including one recalled by the Third Reich’s official architect, Albert Speer — the Fhrer is said to have abhorred the faith for what he deemed its “meekness and flabbiness.” Hitler did, however, fervently worship one thing above all else: the Aryan race. And by the time Hugo Jaeger took the photos seen here, Hitler and Heinrich Himmler, commanding general of the SS, had articulated and launched their plan for creating a “master” race — via, in large part, the extermination of Europe’s Jews.

In 1942, Russian soldiers aim their rifles from behind snow-covered rubble as they defend the Red October metallurgical factory from German troops during the savage, seven-month Battle of Stalingrad. The Germans intended to win the factory as a Christmas present for Hitler; instead, Russian troops held it for the duration of the conflict. The crushing defeat marked the first time the Nazi government acknowledged failure to the German people. As losses mounted and the tide of the entire war began to clearly and inexorably turn against Germany, the Nazis again tried to tweak the meaning of Christmas, celebrating it not as an uneasy melding of resurrected paganism and diluted Christianity, but as a remembrance of the Reich’s fallen. But by the time the long, hard winter of 1942 was half-over, such propaganda had begun to ring hollow.

With beer steins, candles, and traditional holiday garlands set on the table before them, German officers and cadets peer into Hugo Jaeger’s camera at the 1941 Waffen-SS Christmas dinner. Among the more disturbing items on display at the 2009 Cologne exhibition of Nazi Christmas memorabilia: a “Yule lantern,” a Germanic candlestick that had been mass-produced, on Heinrich Himmler’s orders, by the prisoners of the Dachau concentration camp. They were handed out as gifts to to the SS troops — in other words, to men like those seen here.

Here, the one frame from the Christmas party that was published by LIFE magazine in its April 24, 1970, issue. And here, in the caption that ran underneath it, a possible explanation for Hitler’s glum expression: “In 1941, Hitler gave this Christmas party for his generals. Though he dominated his officers and came to despise them, Hitler never felt socially at ease with them — they had better backgrounds and education. He never invited them to dinner, aware that they looked down on the old comrades he liked to have around.”