1930s. Despite these defensive preparations, even the most fortified section of the Mannerheim Line had only one reinforced-concrete bunker per kilometre. Overall, the line was weaker than similar lines in mainland Europe. According to the Finns, the real strength of the line was the "stubborn defenders with a lot of sisu" – a Finnish idiom roughly translated as "guts, fighting spirit". On the eastern side of the Isthmus, the Red Army attempted to break through the Mannerheim Line at the battle of Taipale. On the western side, Soviet units faced the Finnish line at Summa, near the city of Viipuri, on 16 December. The Finns had built 41 reinforced-concrete bunkers in the Summa area, making the defensive line in this area stronger than anywhere else on the Karelian Isthmus. Because of a mistake in planning, the nearby Munasuo swamp had a -wide gap in the line. During the First Battle of Summa, a number of Soviet tanks broke through the thin line on 19 December, but the Soviets could not benefit from the situation because of insufficient co-operation between branches of service. The Finns remained in their trenches, allowing the Soviet tanks to move freely behind the Finnish line, as the Finns had no proper anti-tank weapons. The Finns succeeded in repelling the main Soviet assault. The tanks, stranded behind enemy lines, attacked the strongpoints at random until they were eventually destroyed, 20 in all. By 22 December, the battle ended in a Finnish victory. The Soviet advance was stopped at the Mannerheim Line. Red Army troops suffered from poor morale and a shortage of supplies, eventually refusing to participate in more suicidal frontal attacks. The Finns, led by General Harald Öhquist, decided to launch a counter-attack and encircle three Soviet divisions into a motti near Viipuri on 23 December. Öhquist's plan was bold; however it failed. The Finns lost 1,300 men, and the Soviets were later estimated to have lost a similar number. Battles in Ladoga Karelia The strength of the Red Army north of Lake Ladoga in Ladoga Karelia surprised the Finnish Headquarters. Two Finnish divisions were deployed there, the 12th Division led by Lauri Tiainen and the 13th Division led by Hannu Hannuksela. They also had a support group of three brigades, bringing their total strength to over 30,000. The Soviets deployed a division for almost every road leading west to the Finnish border. The 8th Army