 The Mannerheim Line , an array of Finnish defence structures , was located on the Karelian Isthmus about 30 to 75 km ( 19 to 47 mi ) from the Soviet border . The Red Army soldiers on the Isthmus numbered 250 @,@ 000 facing 130 @,@ 000 Finns . The Finnish command deployed a covering force of about 21 @,@ 000 men in the area in front of the Mannerheim Line in order to delay and damage the Red Army before it reached the line . 
