At the beginning of July, following a discussion with Stalin, Army Gen. G. K. Zhukov initiated planning for an offensive by 20th Army against the Rzhev salient to be called Operation "Sverdlovsk". This was intended primarily as a means to draw German reserves from their developing offensive in the south, but as it developed Zhukov's plan anticipated advances towards Rzhev, Sychyovka and Gzhatsk. In its final form the operation was to include the 29th and 30th Armies of Kalinin Front to the north and the 31st and 20th Armies of Western Front to the south. Kalinin Front began its offensive on July 30, but on the same day heavy rains began which flooded the countryside and turned the roads into quagmires which bogged down the 30th Army's advance while the 29th failed to penetrate the German front at all. After waiting for the weather to abate Western Front attacked on August 4 following a powerful artillery preparation which destroyed or suppressed roughly 80 percent of the German forces' weapons. 8th Guards Corps, in the first echelon of 20th Army, breached the defenses south of Pogoreloe Gorodishche allowing the Army's mobile group, the 2nd Guards Cavalry Corps, to begin to exploit in the direction of Sychyovka. 31st Army was similarly successful to the north and by the end of August 6 the gap in the German front was up to 30km wide and Soviet troops had penetrated to a depth of 25km, closing on the Gzhat and Vazuza rivers.