The 'Vyborg-Keksholm Defensive Operation' was the Soviet response to the Finnish invasion of the Karelian isthmus in the first stage of the 'Jatkosota' continuation war (29 June/23 September 1941).

The object of the Finnish operation was the recapture of the Karelian isthmus, which it had ceded to the USSR on 13 March 1940 by the Moscow peace treaty that marked the end of the 'Talvisota' (Winter War).

The Finnish force facing the Karelian isthmus was Kenraaliluutnantti Erik Heinrichs’s Karjalan Armeija (Army of Karelia), and this comprised a pair of corps disposed in the areas to the north and south of the Vuoksi river: to the north was Kenraalimajuri Taavetti Laatikainen’s II Armeijakunta (corps) and to the south was Kenraaliluutnantti Karl Lennart Oesch’s IV Armeijakunta. The II Armeijakunta consisted of three divisions (Eversti Jussi Sihvo’s 10^th Divisioona, Eversti Niilo Hersalo’s 15^th Divisioona and Eversti Aaro Pajari’s 18^th Divisioona), the 10^th Divisioona having been added after the corps had been ordered to divert Eversti Aarne Blick’s 2^nd Divisioona to operations farther to the north in the Ladoga Karelia region. The IV Armeijakunta' front-line forces were two divisions and one reinforced infantry regiment (Eversti Claes Winell’s 8^th Divisioona and Eversti Einar Vihma’s 12^th Divisioona together with Everstiluutnantti Lauri Pallari’s 25^th Jalkaväkirykmentti (infantry regiment), and its reserve was Eversti Kaarlo Viljanen’s 4^th Divisioona.

The Soviet defence of the Karelian isthmus was based nominally on two separate formations in the form of General Leytenant Mikhail N. Gerasimov’s XIX Corps and General Major Filipp D. Gorelenko’s L Corps. The XIC Corps consisted of two divisions (115^th Division and 142^nd Division), one motorised division (198^th Motorised Division) and one motorised regiment (14^th Motorised Rifle Regiment), and the last of these division was tied down in fighting near Sortavala while the two other divisions held the positions close to the border; the 265^th Division was en route to became the corps' reserve. The relatively quiet Finnish front prompted the Soviet leadership to transfer the command elements of the L Corps to the area lying to the south of Leningrad on 21 July to face the Germans, leaving its divisions (43^rd Division and 123^rd Division) under direct command of General Leytenant Piotr S. Pshennikov’s 23^rd Army. Part of General Leytenant Markian M. Popov’s North Front, the army was tasked with the defence of the approaches to Leningrad.

The II Armeijakunta's advance to the south-east began on 31 July in the isthmus between Lake Ladoga and the Gulf of Finland, but was soon slowed by the Soviet defences and also as a result of the Finnish practice of advancing through forest areas, which caused severe logistical problems. By 14 August the 18^th Divisioona had taken the town and crossing point of Antrea, which left the 115^th Division cut off from the rest of the XIX Corps. The Finnish advance in terrain almost totally devoid of useful roads also slowed the 15^th Divisioona, which managed to capture the town of Hiitola only on 11 August after the 10^th Divisioona had also been brought into the line. The Finnish victory at Hiitola forced the 142^nd Division and 198^th Motorised Division to withdraw into the Kilpola islands group on the XIX Corps' right, and here the Soviets were surrounded into a motti encirclement pinned against the shore of Lake Ladoga. The Finns had cleared the motti by 23 August, but by then 26,000 men had been evacuated from the motti of the Soviet 'pocket' across Lake Ladoga.

Soviet control of the Karelian isthmus close to the south-western shore of Lake Ladoga was crumbling after the defeat of the two Soviet divisions. The 10^th Divisioona ran into the newly arrived 265^th Division on 15 August and, after the battle which followed, encircled the remnants of this Soviet division. A small part of the division managed to escape two days later, but by that time the division’s casualties had already reached to 234 dead, 1,155 wounded and 4,830 missing. Their victories allowed the Finnish forces to act more freely, and the Finns captured the remains of the town of Käkisalmi on 21 August and the village of Taipale on 23 August. The 18^th Division began to cross the Vuoksi river on 17 August and managed to establish a firm bridgehead.

The IV Armeijakunta's primary objective was the city of Viipuri (Vyborg in Russian) on its right flank, and the plan for the achievement of this task was based on the rapid surrounding of the city. However, the Finnish general headquarters did not allow the IV Armeijakunta to embark on the active pursuit of the Soviet forces until 21 August. By this time the 43^rd Division and 123^rd Division had already begun to pull out of their exposed positions close to the border, while the 115^th Division was moving at speed to help contain the Finnish crossing of the Vuoksi river. This meant that the Finnish plan of tying down the Soviets had failed even before it could have been launched. The crossing of the Vuoksi river by the 18^th Divisioona of the II Armeijakunta was assisted by the 12^th Division and Eversti Tiiainen’s 'T' Kevyt Prikaati (light brigade), which comprised the 1^st Jääkäripataljoona (Jäger battalion), two light detachments and two artillery companies of the IV Armeijajunta, which managed to drive a gap through the Soviet line.

Their withdrawal to the narrowest part of the Karelian isthmus allowed the Soviets to exploit their superiority in numbers. The 115^th Division and 123^rd Division were tasked with throwing the Finnish back over the Vuoksi river in an attack which began on 24 August. The attack hit the 'T' Kevyt Prikaati and forced the Finns either to retreat or to entrench themselves. As a result, the Finnish brigade was immobilised and partially surrounded. On 25 August a chance artillery strike killed the commander of the 'T' Kevyt Prikaati, but then the Finnish forces relieving this brigade halted the attack and forced the Soviet divisions to retreat. The IV Armeijakunta started to sever the routes to the south-east from Viipuri. On 24 August the 8^th Divisioona crossed Viipuri bay and cut the coastal route from Viipuri back into the USSR. By 28 August in the Battle of Porlammi, the 43^rd Division, 115^th Division and 123^rd Division and been encircled into a motti around the villages of Sommee and Porlampi.

The Finns had cut all the roads to the motti, but were unable to form a tight blockade in the thick forests, which allowed most of the 115^th Division and 123^rd Division to escape toward Koivisto. However, the bulk of the 43^rd Division was destroyed at the Battle of Porlammi on 1 September. The Finns force marched to the village and port of Koivisto on 2 September, but did not pursue the remnants of the Soviet divisions, which had fled to the islands of the surrounding archipelago: in November, these units were evacuated by the Soviets. While the fighting near Viipuri still raged, the Finnish advance toward Leningrad continued. The IV Armeijakunta was to advance along the western shore, the II Armeijakunta in the centre and Eversti Einar Mäkinen’s newly arrived I Armeijajunta along the eastern side of the isthmus. Mannerheim ordered the Finnish advance to halt short of the Soviet fortifications, and by 31 August these forces had reached the old border, and early in September arrived in front of the the Soviet fortifications and ceased their advance.

On 20 August, General Dr Waldemar Erfurth, a staff officer of the Oberkommando des Heeres and a member of the German liaison staff in Finland, notified Mannerheim that Generalfeldmarschall Wilhelm Keitel was about to send a letter detailing the point at which the Finns were to be asked to attack Leningrad. Mannerheim responded with the practical difficulties of the proposal and presented the Finnish political and military leadership’s opposition to any such attack. The government had decided beforehand that Finland would not attack Leningrad, and it was only after pressure from the military leadership that they accepted a small advance across the old border with the object of taking better defensive positions. The Social Democrat part in particular opposed any crossing the border. When Keitel’s letter arrived, came, President Risto Heikki Ryti and Mannerheim together prepared a negative answer. On 31 August, Erfurth contacted Mannerheim again and proposed that the Finns should cancel the attack into East Karelia, and instead attack Leningrad, but once more Ryti and Mannerheim refused. On 31 August Mannerheim gave the order that the attack be stopped along the line linking Ohta and the mouth of the Rajajoki river. The exact line between Ohta and Lake Ladoga would be determined at a later date after the Finns had reached the old border in that area. That would shorten the front without the need to attack Soviet fortifications to the north of Leningrad in the 2^nd Karelian Fortified Region. In this last phase, the Soviets had six infantry divisions and a number of separate regiments and battalions to defend Leningrad against an attack from the north-west, but all of the Soviet elements were at only half strength as a result of the hard fighting with the Finns.

The 12^th Divisioona had reached its objective by 1 September, but elsewhere the attack started on 2 September. The 18^th Divisioona captured Mainila on this same day and Valkeasaari (now Beloostrov) on the following day. By 7 September both the 18^th Divisioona and the 2^nd Divisioona had reached their targets between the Rajajoki river and Ohta. Mäkinen, the commander of the I Armeijakunta, ordered his men to advance to the line linking Ohta and the Lempaalanjärvi, the old border, at Lake Ladoga with the instruction that, in the event that his troops met strong opposition, the offensive could be stopped there. On 4 September the attack began, and on 6 September the 10^th Divisioona managed to encircle and destroy the Soviet 941^st Regiment at Kirjasalo. Finally, on 9 September the Finns reached their objective line at every point and switched to a defensive posture.

The Soviet military leadership quickly learned of the diminished Finnish pressure, and by 5 September two divisions were already transferred from the Karelian isthmus to the area to the south of Leningrad against the German onslaught from the south. Although the Finnish troops on the Karelian isthmus did not play any active role on the forthcoming siege of Leningrad, their mere presence contributed to the siege by hampering the supply of the city around and across Lake Ladoga.

At the same time as the fighting on the Karelian isthmus, other Finnish forces were committed to an invasion of Ladoga Karelia, the south-eastern part of Finland between the Karelian isthmus and East Karelia round the north-eastern corner of Lake Ladoga. Initially, the Finnish army was deployed in a defensive posture, but on 29 June Mannerheim created the Karjalan Armeija under the command of Heinrichs, and ordered this new formation to prepare to take the offensive into Ladoga Karelia. The new army comprised Kenraalimajuri Paavo Talvela’s VI Armeijakunta with Eversti Ruben Lagus’s (from 25 July Eversti Ilmari Karhu’s 5^th Divisioona and Eversti Kaarlo Heiskanen’s 11^th Divisioona, Kenraalimajuri Woldemar Hägglund’s VII Armeijajunta with Eversti Antero Svensson’s 7^th Divisioona and Eversti Hannu Hannuksela’s 19^th Divisioona, and Kenraalimajuri Woldemar Oinonen’s Ryhmä 'Oinonen' (also known as Ryhmä 'O', Ratsuväkiprikaati (cavalry brigade), 1^st Jääkäriprikaati and 2^nd Jääkäriprikaati). Eversti Paavo Paalu’s 1^st Divisioona was the corps' reserve. The Finnish plan was based on an advance to divide the defending Soviet forces by reaching the north-west shore of Lake Ladoga and then advance along the shore of the lake.

Opposing the VII Armeijakunta was Gorelenko’s 7^th Army with the 168^th Division near Sortavala and the 71^st Division to the north of the Jänisjärvi lake. The Soviets had prepared field fortifications along the border in the area of Sortavala and at the important road junctions at Värtsilä and Korpiselkä.

It was on 9 July that the order to begin the Finnish offensive was given, and the main task of the VI Armeijakunta was to break through the Soviet defences between Värtsilä and Korpiselkä. The Finnish offensive quickly overwhelmed the Soviet defenders. The 1^st Jääkäriprikaati was switched from the Ryhmä 'Oinonen' to spearhead the assault, and this unit opened a gap to the Soviet defences through which Finnish light infantry, some mounted on bicycles, pushed forward.

The right flank of the Finnish offensive, based on the 11^th Divisioona, encountered strong Soviet resistance on the eastern shore of the Jänisjärvi lake, and the clearance of this resistance lasted to 16 July. The 11^th Divisioona then continued its planned advance and rounded the southern end of the Jänisjärvi lake to establish westward-facing positions along the Jänisjoki river. At the same time, Hägglund’s VII Corps had been attacking to the south on the western side of the Jänisjärvi lake, but the determined nature of the Soviet defence made the offensive little more than a crawl. It was thus only on 15 July, therefore, that the Finnish forces reached the main Soviet defences. It took until 17 July for the VII Armeijakunta finally to reach the Jänisjoki river, and clearing the surrounded Soviet forces lasted until 21 July. Since the Finnish advance had extended the front, some of the Finnish forces were starting to redeploy on 16 July, with the 1^st Divisioona being ordered to cover the eastern flank of the advance while Eversti Aarne Snellman’s 17^th Divisioona, which had handed responsibility for the blockade of the Soviet base at Hanko in the north-west coast of the Gulf of Finland to local troops, was also brought into the area. Generalleutnant Erwin Engelbrecht’s two-regiment German 163^rd Division was ordered to capture the town and railroad junction of Suvilahti. These formation adjustments in effect increased the Finnish strength in the area by three divisions.

The advance on the left flank of Talvela’s VI Armeijakunta by the two-brigade Ryhmä 'Oinonen' stalled almost as soon as it had started. Its advance tied down some Soviet troops, but Talvela assessed that the Ryhmä 'Oinonen''s mission had been a resounding failure. However, he also criticised his superior’s orders to use these lighter troops against Soviet positions which were already known to be strong.

The main Finnish advance continued to the south in the direction of Loimola, through which ran the railway linking Sortavala and Petrozavodsk. Loimola had fallen to the Finnish forces by 15 July. Talvela pressed his forces farther and the 1^st Jääkäriprikaati completed its 68-mile (110-km) contested advance when it reached the shore of Lake Ladoga at Koirinoja on the following day. This severed the connections between the Soviet forces in the area. While Talvela’s units continued their advances farther to the east along the shore of the Lake Ladoga as well as farther inland, the Soviets had reorganised some of their forces and were rushing reinforcements to Lake Ladoga’s eastern shore. The 452^nd Motorised Regiment established defensive positions around the town of Salmi, but the Finnish advance encircled the defenders and the Finns had taken Salmi by 21 July. After the VI armeijakunta reached the 1939 border on 23 July, Mannerheim on the next day ordered a halt to any advances farther to the east and set the Finnish forces to the preparation of defensive positions along the Tuulema river. Crossing of the 1939 border did not sit well with all of the Finns, and more than 2,000 men initially refused to set foot across the old border.

The 7^th Divisioona of the VII Armeijakunta launched its attack toward Sortavala from the east and managed to capture the village of Ruskeala on 25 July, so making it possible for the Finns to present a unified front against Soviet forces holding Sortavala. For their part, the Soviets had reinforced the the defence by the 168^th Division with the 198^th Motorised Division and prepared to launch a counterattack toward Jänisjoki river. However, the Finns captured the plan of the Soviet counterattack, and were thus both well prepared and nicely reinforced to repel the Soviet counterattack. By 1 August the 198^th Motorised Division was in full retreat. and the Finnish decision to order the II Armeijakunta to advance trapped the Soviet forces. By 7 August the 2^nd Divisioona of the II Armeijakunta had reached the shore of Lake Ladoga at Lahdenpohja, thus cutting the Soviet divisions to the north-west of Lake Ladoga from their intended lines of withdrawal. Near Sortavala the 2^nd Divisioona, 17^th Divisioana and 19^th Divisioona were reorganised into Eversti Einar Mäkinen’s new I Armeijakunta, and the town fell to the Finns on 15 August. The defending 168^th Division withdrew along the lake shore but were encircled, although the Soviets managed to evacuate most of their men across Lake Ladoga, but had to abandon large quantities of war matériel that was gratefully seized by the Finns.