The Finns planned to attack on both sides of Yanis Lake (Jänisjärvi). They hoped this would split the Soviet defensive line, allowing the Finns to advance along the east shore of Lake Ladoga through Olonets (Aunus) to Lodeynoye Pole (Lotinapelto) on the Svir River. Both IV and II Corps would hold on the border initially but II Corps was to be ready to advance on orders towards the northwest shore of Lake Ladoga.
The Finns commenced offensive operations from the area between Lake Pyha in the southwest and Ilomantsi in the northeast on July 10. The offensive had the conquest of Ladoga Karelia as its objective.14 Small units had operated behind enemy lines before that date. The main Finnish effort was in the VI Corps sector between Vyartsilya and Korpiselkya (Korpiselkä), northeast of Yanis Lake. General Talvela organized two battle groups to cover his flanks. Battle Group South attacked from the area between Lakes Pyha and Yanis with the mission of penetrating the isthmus between Lakes Yanis and Ladoga. Battle Group North was to attack from the area between Korpiselkya and Ilomantsi in the direction of Tolvayarvi (Tolvajärvi) and Muanto.
Despite stubborn local resistance, Soviet defenses quickly collapsed under the weight of the Finnish attack in the Vyartsilya–Korpiselkya sector; and it became apparent that the main Finnish thrust had hit a weak sector in the Russian front. Colonel Ruben Lagus’ 1st Light Infantry Brigade from Group Oinonen was brought in and it managed to break through the Soviet defenses rather quickly.15 Through the gap thus created, the light Finnish infantry, some equipped with bicycles, penetrated deep into enemy territory in the direction of the village of Tolvayarvi. After hard fighting, the town of Kokkari was stormed on July 12 and the village of Tolvayarvi further to the southeast was occupied on the same day. Continuing its exploitation, the light infantry brigade moved on the town of Muanto, which it captured on July 14.
The advance of the right-flank units of VI Corps driving south through Vyartsilya met stiff opposition in the hilly landscape east of Yanis Lake. The VII Corps, expected to advance southward on the west side of Yanis Lake, met heavy opposition and made little progress. Soviet resistance along the east shore of Yanis Lake was eliminated on July 16 and VI Corps swept around the southern end of the lake and set up positions facing west along Yanis River.
Mannerheim ordered several units redeployed on July 16. The 1st Division, which had been his reserve, was ordered forward to protect VI Corps’ eastern flank near Loymola (Loimola). It was commanded by Colonel Paavo Paalu. The 17th Division, which had sealed off Hanko, was moved to the Vyartsilya area. It was commanded by Colonel Otto Snellman. The mission of sealing off the Soviet forces in Hanko was left to coastal defense units and a battalion of Swedish volunteers. Finally Mannerheim committed the German 163rd Infantry Division, commanded by Lieutenant General Erwin Engelbrecht, to the east with the mission of capturing the town of Suvilakhti. This town, located at the southern end of Suo Lake, was a road and railroad junction. By these redeployments Mannerheim effectively increased the forces available to the Army of Karelia by three infantry divisions. The stage was set for a rapid advance towards the Svir River.
While units of the VI Corps secured their positions at Tolvayarvi against possible Soviet attacks from the east, the main body continued southward. General Talvela saw an opportunity and immediately committed all his mobile forces to capture Loymola. This would allow the Finns to interdict the railroad from Petrozavodsk (Petroskoi). A Finnish armored infantry battalion captured Loymola on July 15.
An even more promising opportunity presented itself to General Talvela. This involved a quick thrust to the shores of Lake Ladoga near the town of Koirinoja. A successful drive to the shore of Lake Ladoga would isolate the forces holding Sortavala and contesting the Finnish advance on both sides of Lake Yanis. While flank security forces were sent to the east the bulk of the troops were committed in the direction of Koirinoja on the northeast shore of Lake Ladoga. That town fell to Finnish forces on July 16. Colonel Lagus’ 1st Light Infantry Brigade completed its 110-kilometer contested drive with the capture of Koirinoja.
General Talvela sent two strong columns on a drive towards the east and south. One column was sent eastward to the Tulm Lake area while the main force advanced south along the east shore of Lake Ladoga. The Soviets had reorganized some of its forces and brought in reinforcements from the Karelian Isthmus. Units from the 452nd Motorized Infantry Regiment had reached the front and set up defensive positions around the town of Salmi, where the Tulm River empties into Lake Ladoga. Colonel Lagus’ troops crossed the Tulm River five kilometers north of Salmi, isolating the Soviet defenders. Salmi was captured on July 21 after some heavy fighting and only a small number of the defenders managed to escape the encirclement. The corps crossed the 1939 border on July 23 and on July 24 Mannerheim ordered it to halt along the Tuloksa (Tuulos) River and take up defensive positions.
The Soviet forces facing the Finns on the Ladogan front had reorganized on July 21. The 7th Army had been organized into two groups. One, called the Petrozavodsk Group, was commanded by Lieutenant General M. Antonjuk. Its main combat units consisted of an infantry regiment, two motorized regiments, and an armored regiment. The other group was referred to as Group South under Lieutenant General V. Tsvetajev. It consisted of a marine brigade, two motorized regiments, and some smaller units.
The old border marker erected by King Gustav II Adolphus at Aajakontu was reached by troops of the VI Corps on July 22. General Talvela’s message to Mannerheim reads in part: “After the capture of Manssila today at 1130 hours, the Russians have been chased out of Finland in the operational area of the VI Corps. The area, whose rear boundary is formed by a line Korpiselkä–Jänis River, has been freed from our hereditary foe.”16
The Finnish columns advancing inland from Lake Ladoga were also making good progress. One column crossed the historic boundary on its way to Lake Tulm. The northern settlement on this lake was captured on July 18 and the rest of the settlements along the lake during the following two days. The Soviets put up strong resistance in the Rajakonru area and it was not overcome until July 23 when a Finnish column advancing from the southern part of Lake Tulm towards Vidlitsa (Vitele) threatened the Soviet line of retreat along the shore of the lake. This threat caused the Soviets to withdraw and both Vidlitsa and Rajakonru were taken after light fighting on July 24. The Finnish forces, in accordance with orders from Mannerheim, took up defensive positions.
While the reasons for Mannerheim’s decision to cease offensive operations in Karelia may have been complex, he had ample operational reasons to worry about this front. The rapid advance of the 5th Division along the eastern shore of Lake Ladoga had exposed a 100-kilometer stretch of shoreline in his rear that could be interdicted by the Soviets from the sea. Furthermore, strong Soviet forces were still present in the area north and northeast of Lake Ladoga and in the important Lake Suo area.
Mannerheim’s concerns were soon validated by Soviet actions. Heavy counterattacks by an armored regiment and parts of four infantry regiments in the Vidlitsa area resulted in ten days of heavy fighting before the Finnish front was stabilized about 10 kilometers east of Lake Vidlitsa. Meanwhile, Major General Pavlov, the Soviet commander of the coastal defense forces on Lake Ladoga launched a night amphibious assault in the rear of the Finnish 5th Division at the same time as a strong attack was launched against the Finnish line at Tuloksa. The landing took place on the two small islands of Lukulansaari and Mantsi, just offshore from the town of Salmi. General Talvela had to scrape together whatever forces were at hand, including support troops, in order to keep the Soviets from establishing themselves on the two islands. The Finns were able to destroy four of the 15 ships used in the landing and managed to split the Soviet marines into three encircled pockets, which were eliminated by the evening of July 26. The Soviets made another landing on Mantsi on July 27 and almost succeeded in capturing the islands before enough Finnish forces could be brought in to reinforce the defenders. The fighting was heavy before the Soviet landing force was eliminated on July 28.