Complex sentence: On December 18,1942,6th Mechanized Corps was assigned to the 2nd Guards Army of the Southern Front, where it was involved in stopping the onset of Operation Winter Storm, the Manstein's attempted breakthrough to the Sixth Army stationed in Stalingrad.
Split into simpler sentences: On December 18,1942,6th Mechanized Corps was assigned to the 2nd Guards Army of the Southern Front, where it was involved in stopping the onset of Operation Winter Storm. The Manstein's attempted breakthrough to the Sixth Army stationed in Stalingrad.