 Complete the following phrase:  70th Army was assigned to the re-deploying Don Front soon re-designated Central Front under command of Gen. K.K. Rokossovsky. It was some time before Rokossovsky could knock it into shape as a front-line formation, forcing him to remove many senior, ex-NKVD officers. From 28 February the 70th Army took part in both offensive and defensive operations to the northwest of Kursk. Central Front exploited a gap between the weak Second German Army and the Second Panzer Army, but was brought to a halt by the spring rasputitsa, German reserves released by their evacuation of the Rzhev Salient, and the 