In January 1944, the southern group of German forces in the Ukraine had found themselves in a major crisis. The threat to the entire German front was so serious that Manstein himself would later write that “the situation was similar to that in which the Army Group had found itself during the winter of 1942-43. In fact, the next few weeks would decide whether or not the southern wing of the German armies in the east would be cut off and forced away to the south-west.” The crisis started when Nikolai Vatutin's 1st Ukrainian Front (800,000 men) launched a major offensive west of Kiev on the Christmas Eve of 1943, against Erhard Raus's 4th Panzer Army (360,000 men), belonging to Manstein's Army Group South. Known as the "Zhitomir–Berdichev Operation", this offensive marked the start of the far greater "Dnieper-Carpathian Offensive", which was aimed at smashing Army Group South. Up to 3,500,000 troops in total participated from both sides in this gigantic battle The offensive was in full swing and soon the entire German front, containing the Soviet Kiev bridgehead, began to collapse. Numerous German divisions were already heavily damaged, while the front of the 4th Panzer Army had been split into isolated segments. By mid-January 1944, the Soviets had an almost open road to the southwest and the deep rear area of Army Group South. Now, the biggest and long-standing strategic threat emerged to the army group's left flank. It could take the form of a deep envelopment of most of the Army Group South, carried west to the Carpathians or a shorter southward thrust between the Dnieper and the Dniester rivers. Manstein and OKH, with Hitler's approval, undertook energetic measures to counter this threat. The most significant measure taken was the transfer of the entire 1st Panzer Army from the Southern Ukraine to the northern Ukraine. All told, between 1-14 January 1944, 12 divisions, 2 heavy panzer battalions and 2 assault gun brigades were being brought to the sector held by the 4th Panzer Army. Having amassed sufficient forces, the Germans began to launch a series of counter-offensives against over-extended Soviet armies. One of the main German counter-offensives, named "Operation Vatutin", began in the second half of January. This counter-offensive, in which up to 400 German armored vehicles had participated in, had succeeded in pushing the Soviets back 20-30 km, while also destroying several formations of the Soviet 1st Guards Tank and 38th Armies. As a result, the front-lines had temporarily stabilized. The Soviets advanced 80-200 km, while 8 divisions of the 4th Panzer Army were either destroyed or heavily damaged. The success of this offensive created a new bulge, which the Germans held around Korsun-Schevchenkovsky near the Dnieper. It would be here, where both sides will shift their main focus to in late January 1944, in what will be known as the famous battle of the Korsun-Cherkassy Pocket.