The Finns fall back to the Mannerheim Line

On 1 December 1939, the second day of the Winter War, Soviet aircraft again appeared over Helsinki, while on the Karelian Isthmus the 7th Army was pushing deeper into Finland through deserted, burning villages. The Finnish covering forces made no attempt to stop it at the border. Their task was to delay the enemy’s advance, inflict losses on him, destroy roads and bridges, and then withdraw to the main defensive position, which the world would soon know as the Mannerheim Line. And so it happened: the covering actions lasted less than a week, and by 5–6 December the last Finnish units had passed behind the main fortifications. Popular chronologies say that the Finns fell back “in the first two weeks of the month” to an “obsolete” line. The first statement is an approximation: on the Isthmus the withdrawal was over after six days, although the main Soviet forces were still closing up to the position on its western sector for another week. The second is partly true but needs explaining.

The Karelian Isthmus on 30 November

When the Red Army crossed the border on 30 November, its strongest army struck on the Karelian Isthmus, between the Gulf of Finland and Lake Ladoga. The 7th Army of Komandarm 2nd Rank Vsevolod Yakovlev (PL) had nine rifle divisions, a tank corps and three tank brigades. According to Finnish estimates it numbered some 200,000–250,000 soldiers, nearly 1,500 tanks and armoured cars, and about 900 guns and mortars. Its task was to break through the Finnish defences quickly, take Viipuri (Vyborg) and move on Helsinki. The pretext for the attack was the Mainila incident of 26 November, and the commander of the Leningrad Military District, Komandarm 2nd Rank Kirill Meretskov, gave assurances that the war would last about two weeks.

The Isthmus was defended by the Army of the Isthmus under General Hugo Österman, some 130,000 men strong. Its II Corps under General Harald Öhquist held the western part of the Isthmus, from the Gulf of Finland to the Vuoksi river, with the 4th, 5th and 11th Divisions on the main position, while III Corps under General Erik Heinrichs held the eastern part, from the Vuoksi to Ladoga, with the 8th and 10th Divisions. In front of the main position, in a belt several dozen kilometres deep, some 21,000 soldiers of the covering forces were deployed, divided into four groups: Uusikirkko on the Gulf of Finland, Muolaa and Lipola in the middle of the Isthmus, and Rautu in the east. They were made up of border guard, Jäger and reservist battalions, supported by a handful of guns.

Originally the covering forces were meant to buy time for mobilisation. But since Finland had already mobilised its army in October under the name of “extraordinary reserve exercises”, and the divisions had been in their positions for weeks, headquarters changed their task: they were to bleed and slow the advancing columns before these reached the main line of defence.

Covering actions and scorched earth

The Finnish command prepared the Isthmus for defence by a method now known as scorched earth. The population of the border communes had been evacuated inland back in the autumn. As the covering forces fell back, sappers blew up bridges, mined the roads and blocked them with felled trees, and soldiers set fire to houses, barns and farm buildings so that the enemy would have no shelter from the frost. The border resort of Terijoki, where on 1 December Moscow announced the creation of the puppet “people’s government” of Otto Kuusinen, was taken by the Red Army without a fight and largely burnt out.

The Soviet columns advanced slowly. Their vanguards ran into ambushes at every neck of land between lakes and at every forest edge, and the sappers lost hours clearing obstacles and mines. Finnish soldiers opened fire at close range, withdrew on skis to the next position and did the same again a few kilometres further on. The Soviet infantry, poorly trained and ill-prepared for fighting in a winter forest, kept to the roads, and many commanders were afraid to send their men into unknown terrain.

Tanks turned out to be the Finns’ biggest problem. The Finnish army had very few anti-tank guns, and most soldiers had never seen an armoured vehicle up close. In the first days there were cases of panic, which the Finns called “tank fright”, when sub-units abandoned their positions at the sight of approaching machines. It quickly became clear, however, that tanks moving without infantry cover were defenceless against determined men acting at close quarters. Soldiers jammed logs and crowbars between the wheels and tracks, threw bundles of grenades and demolition charges and, above all, bottles of inflammable mixture, soon to be called “Molotov cocktails” (incendiary bottle). According to Finnish tallies, some 80 Soviet tanks were destroyed in the covering actions on the Isthmus. The experience of those days became the basis of the anti-tank methods the Finns used until the end of the war.

Finnish losses were small. According to the Finnish history of the war, the covering forces lost some 400 men in less than a week, including more than 130 killed and about 80 missing; among the missing were some twenty soldiers of one battalion who went over to the Soviet side in the first days. The covering actions could not halt the Soviet offensive, but they delayed it enough that the 7th Army reached the main defensive position worn out, with overstretched supply lines and without proper reconnaissance of the Finnish fortifications.

Behind the main position

On 5 and 6 December the last Finnish covering units passed behind the main position and were sent into reserve. The front on the Isthmus settled on a line running from the Gulf of Finland through lakes Kuolemajärvi and Muolaa to the Vuoksi, and then along the Vuoksi, Lake Suvanto and the Taipale river to Ladoga. At the eastern end, on the Taipale, Soviet divisions reached it fastest, because the road from the border was shortest there, and launched their first attacks as early as 6 December. In the west, on the Viipuri axis, the main forces of the 7th Army were still closing up to the line over the following days, probing it in combat and bringing up artillery. The first great assault on the Summa sector came only in mid-December.

North of Lake Ladoga the Finnish units fell back for longer. The 8th Army pressed along the lake shore and through Suojärvi, and the Finnish command went through moments of serious alarm there in the first week. The retreat was halted only in the second week of December, and in that sense the phrase about a “two-week” retreat describes the situation on the front as a whole better than on the Isthmus alone.

What the Mannerheim Line was

The Finnish army never officially used the name “Mannerheim Line”. It spoke of the “main position” on the Isthmus. The name was reportedly coined by Jorma Gallen-Kallela, son of the painter Akseli Gallen-Kallela, and was popularised by foreign journalists, who linked the fortifications with the name of the Commander-in-Chief, Marshal Carl Gustaf Emil Mannerheim.

The position was about 130–140 kilometres long, of which roughly 80 kilometres rested on lakes and rivers. It was built in two stages. In 1920–1924 more than eighty small machine-gun casemates and a few gun emplacements were constructed. They were cast from unreinforced, low-strength concrete, which protected against small-arms fire and light artillery but not against heavy shells. Many of them fired straight ahead through wide embrasures that were easy to spot and to engage. When the Chief of the General Staff, General Oscar Enckell, resigned in 1924 over disputes about money, construction stopped. It resumed in the 1930s, but for lack of funds the army built only two or three modern bunkers a year. The strongest bunkers were built in 1936–1939 near the village of Summa, on the road to Viipuri, which was considered the most threatened axis. One of them, which cost more than a million marks, was nicknamed the “Million”. Some of the old casemates were rebuilt, with their frontal embrasures bricked up and flanking ones added.

According to Finnish tallies, when the war broke out there were some forty concrete machine-gun bunkers on the main position, only some of them modern, and a few artillery emplacements. According to Finnish calculations, a little over 14,500 cubic metres of concrete went into the whole line – less than a single building, the Helsinki opera house, consumed half a century later. Only a few of the bunkers had armoured observation cupolas and good ventilation. The line had no underground connections and no heavy guns in turrets. The comparison with the French Maginot Line, which Soviet propaganda soon spread to explain the Red Army’s defeats, was entirely misplaced.

The real strength of the position lay in its field fortifications, built in haste in the summer and autumn of 1939, largely by volunteers: students, workers and members of defence organisations. More than 600 timber-and-earth machine-gun nests and dugouts were built on the main position, along with more than 330 kilometres of barbed-wire entanglements and some 136 kilometres of anti-tank obstacles made of boulders weighing several tonnes. Trenches, ditches and obstacles were laid out to exploit the lakes, swamps and forests, which forced an attacker to assault across narrow necks of land under crossfire. On the flanks the line was supported by coastal artillery fortresses on the Gulf of Finland and on Ladoga. There were, however, gaps: on the Munasuo swamp near Summa, through a designers’ error, a kilometre-long stretch was left almost without fortifications.

In this sense the word “obsolete” is true only of the concrete casemates of the 1920s. The Mannerheim Line was neither a modern fortress nor a worthless relic. It was a belt of field defences, supported by a sparse network of bunkers and superbly fitted to the terrain, designed not so much to repel the enemy as to bleed him and bring him to a halt. Its value depended on its defenders and on pre-registered artillery fire – though the artillery suffered from an acute shortage of ammunition.

Bombs over Helsinki

On the first day of the war Soviet aircraft bombed Helsinki three times. The heaviest raid, in the afternoon, fell on the city centre and killed 91 people. On 1 December Soviet aircraft appeared over the capital again, although this time the raid did not cause comparable destruction, and according to tallies by Helsinki historians all the fatalities of the first two days died on 30 November. In the first days of the war bombs also fell on other towns, above all Viipuri, and on railway junctions and ports.

Then the weather worsened and the raids on the capital stopped for almost three weeks. The authorities used this time to evacuate: of Helsinki’s roughly 250,000 inhabitants, about 65,000 remained in the city over the following weeks. Further raids on the capital came on 19 and 25 December and in January. That same 1 December also brought a change of government in Helsinki: the cabinet of Aimo Cajander gave way to the government of Risto Ryti, which sought a way to open talks, but Moscow now recognised only the “people’s government” in Terijoki.

Place in the war

The withdrawal to the main position ended the first stage of the fighting on the Karelian Isthmus. The Soviet plan assumed that the 7th Army would pass through the Finnish fortifications on the march. Instead, in the very first days of December, its divisions – tired, badly led and surprised by the resistance – came up against a line they had not reconnoitred and did not know how to attack. The December assaults on the Taipale and at Summa collapsed with heavy losses, and at the end of December Stalin halted the frontal attacks. The Mannerheim Line held until February 1940. It was broken only on 11 February at Summa, after weeks of preparation and with the use of many times greater forces and heavy artillery.

The legend of the line outlived its bunkers, which Soviet sappers blew up after the Moscow peace in March 1940. For decades Soviet historiography portrayed it as a fortress comparable to the Maginot Line in order to justify the losses. The Finns drew the opposite conclusion from the war, and in 1940–1941 they built the far more solid Salpa Line further west, along the new border, and during the Continuation War further positions on the Isthmus. In June 1944 the Red Army broke through them within a few days with an overwhelming superiority in artillery and aircraft. The experience gained in the first days of December 1939, when Finnish soldiers learnt to destroy tanks with bottles and bundles of grenades, became part of the legend of the Winter War, and the picture of a helpless Red Army in front of the Mannerheim Line confirmed Hitler in his belief that the Soviet Union was weaker than it really was.