 Although the Karelian Isthmus front was less active in January than in December , the Soviets began increasing bombardments , wearing down the defenders and softening their fortifications . During daylight hours , the Finns took shelter inside their fortifications from the bombardments and repaired damage during the night . The situation led quickly to war exhaustion among the Finns , who lost over 3 @,@ 000 men in trench warfare . The Soviets also made occasional small infantry assaults with one or two companies . Because of the shortage of ammunition , Finnish artillery emplacements were under orders to fire only against directly threatening ground attacks . On 1 February , the Soviets further escalated their artillery and air bombardments . 
