The Red Army attacks the Mannerheim Line

In the first week of December 1939 the Soviet 7th Army, which had invaded Finland on the Karelian Isthmus on 30 November, came up against the main Finnish defensive position, which the world’s press was already calling the Mannerheim Line. The Soviet command expected to pass through it on the march and to stand before Viipuri (Vyborg) within a few days. Throughout December, however, one assault after another – first on the Taipale river at the eastern end of the Isthmus, then at the village of Summa on the road to Viipuri – broke down under the fire of Finnish artillery and machine guns. By Christmas the Red Army had lost thousands of men and dozens of tanks without taking a single important point of the Finnish defences.

5, 6 or 17 December?

War chronologies usually state that on 5 December 1939 the Russians “launched heavy attacks on the Mannerheim Line”. This is a simplification. Until 5 December the fighting on the Isthmus was conducted by covering forces, which, in accordance with the Finnish plan, were falling back to the main position, burning villages and blowing up bridges. The first blow against the line itself came on 6 December, Finland’s Independence Day, on the Taipale river. On the western, more important part of the Isthmus the leading units of the 7th Army made contact with Finnish outposts the same day, but they came up to the main position only around 12 December, and made their first great attempt at a breakthrough at Summa on 17 December. The heaviest assaults on the Taipale, which some chronologies record under 15 December, came on 15–17 December. The first, December assault on the Mannerheim Line thus began on 5–6 December and ended in the last days of the month.

The line and its defenders

The Mannerheim Line was not the Finnish equivalent of the Maginot Line that Soviet propaganda made it out to be. It cut across the Karelian Isthmus for about 130–140 kilometres, from the Gulf of Finland to Lake Ladoga, and roughly half of that length rested on lakes and rivers: in the east on Lake Suvanto, the Vuoksi river and its outlet branch, the Taipaleenjoki. According to Finnish calculations, at the start of the war the main position had only a few dozen concrete machine-gun bunkers, among them more modern structures concentrated around Summa and older ones, built back in the 1920s, in the east of the Isthmus. The whole line used about 14,500 cubic metres of concrete. The rest consisted of fire trenches, earth-and-timber emplacements and dugouts, hundreds of kilometres of barbed-wire entanglements and rows of anti-tank boulders, largely put in place in the summer and autumn of 1939 by volunteers and reservists. The line’s strength lay in its use of the terrain, camouflage, pre-arranged artillery fire plans and the soldiers who manned it.

The Isthmus was defended by the Army of the Karelian Isthmus under General Hugo Österman. In the west, between the Gulf of Finland and Lake Muolaanjärvi and on to the Vuoksi, stood II Corps under General Harald Öhquist, with the 5th Division covering the Summa sector. The eastern part of the Isthmus was held by III Corps under General Erik Heinrichs, with the 10th Division on the Taipale. Behind them the 6th Division waited in the reserve of the Commander-in-Chief, Marshal Carl Gustaf Emil Mannerheim. The weakness of the defence was the lack of anti-tank guns and of artillery ammunition, which had to be husbanded from the first day.

Facing them was the 7th Army of Komandarm 2nd Rank Vsevolod Yakovlev (PL): according to Finnish studies, nine rifle divisions and a tank corps, in all nearly 200,000 men, about 1,500 tanks and armoured vehicles and about 900 guns and mortars. Its main objective was Viipuri, and beyond it Helsinki. In the east of the Isthmus, on the Taipale, operated the so-called right-wing group of Komkor Vladimir Grendal, a Finnish-born artilleryman of the old Tsarist army.

Taipale: the first blow

On 3 December Grendal received orders to break through the defences in his sector. The choice of the eastern flank was meant in part as a diversion; Mannerheim, however, was not deceived and did not weaken the Summa sector. On the morning of 6 December, after a bombardment lasting several hours, the Soviet 49th Rifle Division crossed the Taipaleenjoki in boats, including rubber pontoons, and seized a bridgehead on the Koukunniemi headland, a flat, open piece of land surrounded by water on three sides. The Finnish 28th Infantry Regiment, made up of inexperienced reservists, failed to throw the attackers back into the river. Two counter-attacks on 7 December, the first launched in darkness at 5 a.m., broke up into isolated skirmishes, and the Finns withdrew to the main position at the base of the headland. The Koukunniemi bridgehead remained in Soviet hands until the end of the war, but the Red Army got no further.

Over the following days Soviet artillery shelled the Finnish trenches while the infantry made reconnaissance attacks. On 10 December a regiment of the 150th Rifle Division attacked the positions at Kirvesmäki and lost almost all its battalion and company commanders. The only gain was a concrete bunker forward of the line, which the Finns called the Alcázar. The Finnish command meanwhile reorganised the defence: the sector was divided between the 30th and 23rd Infantry Regiments, and the exhausted 28th Regiment was withdrawn into reserve.

15–17 December: the assault on the Taipale

The main assault on the Taipale began at 8.30 a.m. on 15 December with a heavy artillery bombardment. Before noon the infantry went in with T-26 light tanks of Colonel Dmitry Lelyushenko’s 39th Tank Brigade, which had been ferried across to the bridgehead a few days earlier. The tanks manoeuvred badly on the hilly bank cut by streams, and Finnish machine guns separated them from their infantry. According to a Russian study, of the 59 vehicles that took part in the attack, 28 were lost that day and more the next. Finnish sources speak of about thirty tanks appearing on the north bank of the river for the first time. Those that broke through the line were destroyed at close range with bundles of grenades and incendiary bottles. Here and there the attackers broke into the trenches, but on 16 December Finnish counter-attacks restored the whole position.

On the morning of 17 December the fresh 150th Division was preparing to attack. The Finnish artillery, supported in this sector also by the guns of coastal batteries on Ladoga, pre-empted it with concentrated fire on its assembly area, and the attack barely got under way. Soviet soldiers had to advance across open fields and ice under the fire of guns that the Finns had had ranged in for months. On the heaviest days, according to Finnish calculations, up to 15,000 shells a day fell on the Finnish positions on the Taipale. Even so, the 10th Division held the line. No other sector of the Finnish front was shelled so long and so heavily throughout the war as the Taipale.

Summa: tanks without infantry

In the west of the Isthmus the Soviet command was meanwhile undergoing changes. On 9 December operations against Finland were placed under the Headquarters of the Main Military Council in Moscow, with Joseph Stalin, the People’s Commissar for Defence Kliment Voroshilov and the Chief of the General Staff Boris Shaposhnikov, and command of the 7th Army was taken over from Yakovlev by Komandarm Kirill Meretskov himself, commander of the Leningrad Military District. Meretskov directed the main blow exactly where the Finns expected it: at Summa, a village on the road and railway from Leningrad to Viipuri, and at the neighbouring road junction of Lähde, by the Munasuo swamp. It was the most heavily fortified sector of the line, but also the shortest route to the objective.

On 16 December the Soviet artillery began its preparation, and on 17 December, after hours of bombardment and air raids, tanks went into the attack with the infantry of the 123rd and 138th Rifle Divisions. With them went into action a company of experimental heavy tanks of the 20th Tank Brigade: prototypes of the twin-turreted SMK and T-100 and the single-turreted KV. The brigade’s main strength consisted of triple-turreted T-28s. In the Munasuo sector some 20 tanks drove across the Finnish trenches, but the infantry followed them slowly and, under machine-gun fire, went to ground in front of the wire. The hardest day came on 19 December, when the weather improved and the Russians could use observation balloons and aircraft. According to Finnish estimates, the attack was supported by about a hundred tanks. At Summa the vehicles penetrated almost two kilometres into the defences and were stopped only by a minefield; along the road to Lähde they got as far as the support line behind the main position.

Finnish soldiers, who had nothing with which to fight tanks, let them pass and stayed in their trenches to cut off the infantry following behind. Deprived of cover, the tanks circled behind the line, firing at bunkers and emplacements, and after dark they either went back or fell prey to Finnish squads armed with bundles of grenades, demolition charges and incendiary bottles. The SMK ran over a mine and was stranded behind the Finnish line. In the evenings Finnish reserves drove the Soviet infantry out of the lost stretches of trench. On 20 and 21 December the attacks weakened, and on 21 December the 5th Division recovered the last strongpoints taken by the Russians. Fifty-two destroyed tanks, ten of them heavy, were counted in front of its positions, and more stood inside the Finnish lines. The First Battle of Summa, which lasted from 17 to 22 December, ended in a Finnish defensive victory – a surprisingly easy one, as Finnish historians later noted: the division did not even have to commit higher reserves.

The reasons for the Soviet defeat were clear even then. Tanks, artillery and infantry fought separate battles. The artillery fired to a plan and a timetable rather than at reconnoitred targets, and even bombardments of thousands of shells did not destroy concrete bunkers. The infantry did not know how to follow the tanks or how to breach wire. Commanders, thinned out by the Great Purge, were afraid to depart from their orders and repeated failed attacks in the same places. The cold could not be blamed: according to Russian archival research, until 20 December temperatures on the Isthmus ranged from +1 to –23 degrees Celsius, and the snow cover was some ten to twenty centimetres deep. The great frosts came only in January.

The Finnish counter-attack of 23 December

The success of the defence encouraged the Finnish command to try to exploit it. The staff of II Corps, with Österman’s consent, hastily prepared a counter-attack codenamed Verhous. The 1st and 6th Divisions were to strike from two directions – from the area of Muolaanjärvi and from beyond the small Summajoki river – and encircle three Soviet divisions and two tank brigades standing in front of the Finnish line. At 6.30 a.m. on 23 December, without artillery preparation in order to surprise the enemy, the Finnish battalions left their trenches. The plan failed. Some units lost their way on the night march and did not arrive in time, communications broke down, and reconnaissance had greatly underestimated the Soviet forces, which turned out to be not exhausted remnants but strong and well dug in. When the sky cleared in the morning, the Finns came under fire from Soviet artillery and aircraft. At 2.30 p.m. Öhquist called off the attack, and the units returned to their start lines. The Finns lost 361 killed, 777 wounded and 190 missing, 1,328 men in all. Soviet losses were estimated to be similar. The failure convinced Mannerheim that his army was incapable of conducting large offensive operations on the Isthmus. Finnish historians point out, however, that the counter-attack delayed the next offensive the Russians were preparing at Summa.

On Christmas Day, 25 December, the Red Army tried once more in the east. The fresh 4th Rifle Division crossed the ice of Lake Suvanto in darkness and a snowstorm and seized several bridgeheads near the villages of Kelja, Volossula and Patoniemi, in the rear of the Finns defending the Taipale. The Finnish artillery cut them off from reinforcements, and within three days counter-attacks had destroyed the units that had crossed. The ice of the lake was covered with hundreds of bodies. At Kelja alone the Finns counted some 2,000 enemy dead and captured, among other things, 12 anti-tank guns and 140 machine guns – weapons they were short of. The last major attacks at Summa, on 27 and 28 December, were also repulsed. On 26 December the 7th Army suspended offensive operations, and its soldiers began building field fortifications. Soon afterwards the troops in the east of the Isthmus were formed into the 13th Army, commanded by Grendal.

Place in the war

The December attacks on the Mannerheim Line ensured that the war would not end in the swift march on Helsinki that Stalin had expected. Instead a stalemate lasting several weeks set in on the Isthmus, and Soviet propaganda, to explain the defeat, began describing the Finnish fortifications as more formidable than the Maginot Line. This myth survived in Soviet textbooks and in some Western books for decades. At the same time, in the very days when the Soviet assaults were collapsing at Summa and on the Taipale, Finnish units in the forests north of Lake Ladoga and in central Finland began to win their first victories over road-bound divisions – at Suomussalmi, on the Kollaa and at Tolvajärvi.

The Kremlin drew its lessons from the December defeat. On 7 January 1940 the North-Western Front was formed under the command of Komandarm 1st Rank Semyon Timoshenko. Tens of thousands of soldiers, heavy artillery and new tanks were brought to the Isthmus, and the troops practised cooperation between infantry, tanks and sappers on mock-ups of the Finnish fortifications. The new offensive began on 1 February 1940, and on 11 February, after a massive bombardment, the Soviet 123rd Division – the same one that had failed to get through the trenches at Lähde in December – broke through the Mannerheim Line at the very same spot. On the Taipale the Finns held out until the end of the war, but with Viipuri threatened, Finland accepted the Soviet peace terms in March 1940. The experience of Summa also gave birth to the KV tank, adopted by the Red Army as early as 19 December 1939, which in the summer of 1941 was to take the Germans by surprise.

The December failures had another consequence, however, that Stalin had not foreseen. The picture of the Red Army helplessly assaulting Finnish trenches confirmed Adolf Hitler and his generals in their belief that an army weakened by the purges was weak and could be defeated in a single short campaign. This assessment weighed heavily on the planning of the attack on the Soviet Union in 1941.