Following the catastrophic capitulation of the German 6th Army at Stalingrad, an even greater disaster loomed for the German southern wing of the Eastern Front in the early part of 1943. Between Voroshilovgrad and Belgorod, a 200-mile wide gap had been opened in the German front line following the collapse of the Allied Armies. 

Strong Russian mobile forces from the Voronezh and South Western Fronts had been driving into this gap since the beginning of January, with the aim of crossing the Donets River, striking towards Kharkov and then onwards to the Dnepr River. Meanwhile the Southern Front was advancing towards Rostov and threatening to cut off German forces to its east. The crisis point had arrived for the German forces in the south. Army Group Don was in danger of...