 The main focus of the Soviet attack was switched to the Karelian Isthmus . Timoshenko and Zhdanov reorganised and tightened control between different branches of service in the Red Army . They also changed tactical doctrines to meet the realities of the situation . All Soviet forces on the Karelian Isthmus were divided into two armies : the 7th and the 13th Armies . The 7th Army , now under Kirill Meretskov , would concentrate 75 % of its strength against the 16 km ( 9 @.@ 9 mi ) stretch of the Mannerheim Line between Taipale and the Munasuo swamp . Tactics would be basic : an armoured wedge for the initial breakthrough , followed by the main infantry and vehicle assault force . The Red Army would prepare by pinpointing the Finnish frontline fortifications . The 123rd Assault Division then rehearsed the assault on life @-@ size mockups . The Soviets shipped massive numbers of new tanks and artillery pieces to the theatre . Troops were increased from ten divisions to 25 – 26 divisions , six or seven tank brigades and several independent tank platoons , totalling 600 @,@ 000 men . On 1 February , the Red Army began a massive offensive , firing 300 @,@ 000 shells into the Finnish line in the first 24 hours of the bombardment . 
