It began its involvement in the Russian Campaign as the spearhead of Army Group South. Shortly after being promoted to Field Marshal, von Reichenau died in an aircraft accident while being transported to a hospital after a heart attack in January 1942. He was succeeded by his former chief of staff, General der Panzertruppen Friedrich Paulus. Paulus led the 6th Army to a major victory at the Second Battle of Kharkov during the spring of 1942. This victory sealed the 6th Army's destiny because it was selected by the OKH for the attack on Stalingrad. The 6th Army failed to obtain a quick victory; winter came and with it Operation Uranus -- the massive attack of Soviet forces on the flanks of the German corridor between the Don and Volga rivers in November 22-23. The 6th Army was isolated and a major relief operation, (Operation Wintergewitter), which eventually failed, was undertaken by Field Marshal Erich von Manstein. Paulus was promoted by Hitler to the rank of Generalfeldmarschall on January 31, 1943 ostensibly in part because until that day no German Field Marshal had ever surrendered. In other words, Adolf Hitler expected Paulus to commit suicide, but Paulus soon surrendered to the Soviet Forces, contrary to orders by his political chief. The remaining forces of the 6th Army, under the independent command of General Karl Strecker, surrendered three days after in the Tractor Factory, at the north of Stalingrad. Although that was not the definitive end of the 6th Army on this occasion, it was one of the worst military disasters in German history. For the first time, an entire German field army had been completely destroyed.

http://en.wikipedia.org/wiki/German_Sixth_Army#Eastern_campaign