The rapidity of the Finnish advance—particularly that of the 12th Division—kept the 23rd Soviet Army from carrying out its plan to make a stand in the vicinity of the old Mannerheim Line. They continued their fighting withdrawal towards the lower part of the Karelian Isthmus. Finnish forces continued their advance across the Karelian Isthmus in the direction of the town of Koivisto (Primorsk) without encountering serious opposition. Units of IV Corps reached the old border on August 31 and Koivisto on September 2.
The Finnish advance along the western shore of Lake Ladoga towards the old border had also continued. Mannerheim shifted I Corps headquarters, under Major General Einar Mäkinen, from Sortavala to the eastern part of the Karelian Isthmus on August 24. It was assigned two divisions from II Corps—the 10th and 15th—and given the mission of clearing the Ladoga side of the isthmus south of the Vuoksi River. It reached the border on August 31, as did the 2nd Finnish Division. The whole stretch of the old border was secured by September 2.
In a one-month offensive the Finns had driven the 23rd Soviet Army out of Finland and recaptured their lost territory on the Isthmus of Karelia. Only a few islands off Koivisto and in Lake Ladoga were still in Soviet hands. The islands of Valaam and Konevitsa on Lake Ladoga were captured at the end of September 1941.
Mannerheim and the Finnish government now had to consider whether their offensive should stop at the border or, as the Germans pressed for, continue southward. This question had both political and military ramifications. There was opposition within the Finnish government, particularly from the Social Democrats, to continuing the offensive past the border on the Karelian Isthmus. These opponents also wanted to rein in Mannerheim’s offensive plans for East Karelia. This split was reflected in the cabinet. Blücher, the German ambassador to Finland, claims that this opposition was just a passing thing and that the Finnish cabinet almost immediately returned to favoring an aggressive pursuit of the war.20
Mannerheim had already decided, on September 1, that the offensive should continue across the frontier far enough that his troops would be able to occupy favorable defensive positions. The new, more defensible line ran from the mouth of Sestra (Rajajoki) River northeast to Lake Ladoga—basically a diagonal line a short distance north of the towns of Sestroretsk and Agalatovo. There was little fighting involved in moving to the new positions except a sharp engagement in the sector of I Corps where the 10th Division managed to encircle and destroy the 941st Soviet Infantry Regiment. The whole length of the new defensive line had been reached by September 9.
Up to this point, the Finns had basically recaptured territories taken from them during the Winter War. While their forces had crossed the pre-1940 borders in some places, particularly in Ladoga Karelia and the area to the west of Seg Lake (Seesjärvi), those incursions into pre-1940 Soviet territories could be justified on military grounds as providing flank protection or as an attempt to obtain positions better suited for defense. This all changed with the commencement of what is commonly referred to as the East Karelian offensive, in September 1941.
Offensive operations into East Karelia had actually begun before the Ladoga Karelia offensive. The unit undertaking this operation was the 14th Finnish Division, under the command of Colonel Erkki Raappana. It began its operations from the Lieksa area, approximately 200 kilometers north of the northernmost point of Lake Ladoga. The 14th was not part of the Army of Karelia, but a separate division answering directly to Mannerheim.
The 14th Division formed a link between the Army of Karelia operating against the Svir River and the III Finnish Corps, which was part of the Army of Norway. The border between the Finnish and German sectors ran southwest from Lake Oulujärvi in Oulu Province to the border. This link was rather tenuous since large tracts of virgin, roadless forests separated it from both the Army of Karelia and the right flank of the Army of Norway. While a north–south railroad running from Oulu on the Gulf of Bothnia to Sortavala and on to Helsinki came within 20 kilometers of the border in the 14th Division’s area, there was no east–west railroad and the east–west roads in the area were few and can hardly be described as roads. The 14th Division was therefore in a difficult logistic position and had to rely on its own resources.
Mannerheim directed Colonel Raappana to advance eastward to the town of Rugozero (Rukajärvi) on the road to Kotshkoma on the Murmansk Railroad. Colonel Raappana initiated operations several days before the Army of Karelia in the south opened its offensive against Ladoga Karelia. Patrols crossed the border on July 1 and the main advance began two days later. The Soviet forces that initially opposed the advance of the 14th Division consisted of the 337th Infantry Regiment of the 54th Soviet Infantry Division and the 73rd Border Guard Detachment.
The 14th Division captured Reboly (Repola) on July 6 and the advance continued. The Finns crossed Lake Leksozero (Lieksajärvi) northeast of Reboly on July 11. The village of Lendery was captured by another column. The advance in the wilderness was slow because the 14th Division lacked light infantry. Nevertheless, it managed to score a brilliant tactical victory by encircling major Soviet forces in the isthmus areas of this lake country. The encirclement at Omelia was completed on July 23 and Soviet attempts to break out of the pocket were only partially successful. Over 100 drowned in an attempt to cross one of the lakes and 300 were captured. The troops in the encirclement surrendered on July 24.
The 14th Division encountered stiff resistance at the Ontrosenvaara Hills west and south of Rugozero. The fighting for these hills took place between July 30 and August 12. The Soviets had brought in reinforcements in the form of the 137th Regiment from the 54th Division and the 71st Border Guard Detachment. These forces were unable to halt the Finnish advance and a new Soviet division—the 27th—was formed. The Soviets had well-prepared positions at the Rukavaara Hill and were able to halt the Finnish advance for three weeks.
The Finns initiated an encirclement of the Rukavaara Hill, forcing the Soviets to abandon their positions on September 8. Rugozero was captured on September 11. The 14th Division had accomplished the mission assigned it by Mannerheim with comparatively small losses. The division crossed the Onkajoki River just east of Rugozero and took up defensive positions.
At the beginning of September 1941 the Army of Karelia was deployed with Group Oinonen on the left from the 1939 border to Syam (Syamozero) Lake. The Group consisted of one cavalry brigade and the 2nd Light Infantry Brigade. The VII Corps was located just east of Lakes Syam and Vedlo. It consisted of two divisions—the 1st and 4th. The VI Corps, consisting of three divisions (5th, 17th, and 7th) and the 1st Light Infantry Brigade, was located on the right between Vedlo Lake and the point where the Tuloksa River empties into Lake Ladoga. The 163rd Division was located behind the VI Corps as Mannerheim’s reserve.
The offensive began on the night of September 3–4, with the heaviest artillery preparation of the war. This allowed the 5th Division of VI Corps to cross the Tuloksa River seven kilometers from the coast. Finnish units managed to cut the coastal road by noon on September 4 but were hit by a Soviet counterattack, which created a dangerous situation until the corps reserve was committed. After blunting the Soviet counterattack the Finns drove to the shore of Lake Ladoga behind the Soviet defenders along the south bank of Tuloksa River. The trapped Soviet forces—3rd Marine Brigade and two infantry regiments—were practically destroyed.
The successful attack by the 5th Division opened the road to Olonets for Colonel Lagus’ Task Force—1st Light Infantry Brigade and one infantry regiment. The task force passed through the 5th Division and captured Olonets after a brief fight on September 7. A Finnish detachment from Task Force Lagus continued the eastward advance and captured the northern end of the railroad bridge at Svir Station on September 8. This severed the rail connection between Murmansk and Volkhov and took place on the same day as Army Group North captured Schlusselburg in the southwest corner of Lake Ladoga.