The front between the Gulf of Finland and Lake Pyha was relatively quiet during the month of July. The discussions at Finnish Headquarters about action on the Karelian Isthmus assumed increasing importance towards the end of the month. General Erfurth notes that Mannerheim was not prone to make hasty decisions and observes that the inactivity of the Finns west of Lake Pyha allowed the Soviets to shift forces not only against the approaching German Army Group North but also to move forces to the area east of Lake Ladoga to contest the advance of the Army of Karelia.18
Mannerheim ordered General Laatikainen’s II Corps to begin its attack on July 31. The initial phases of this attack were related under the Army of Karelia offensive since its mission to clear the northwest shore of Lake Ladoga was more in support of the operations of that army than a separate offensive on the Karelian Isthmus. Nevertheless, by capturing Khitola and reaching the shore of Lake Ladoga between Kegsgolm and Khitola on August 11, the forces were in an ideal position to continue their advance southward on the Karelian Isthmus.
Ziemke writes that “the Finnish plan of operation underwent a fundamental change” during the first half of August.19 He notes that General Erfurth, the German liaison officer at Mannerheim’s headquarters, had reported as early as July 14 that he had detected opposition on the part of Mannerheim to operations east of Lake Ladoga but that this warning had been dismissed by OKH. That headquarters changed its mind in early August. On August 2, OKH requested that the Finns resume their offensive towards Lodeynoye Pole to coincide with the final push towards Leningrad by Army Group North. Mannerheim refused and in his reasoning shifted the blame back to the Germans by stating that the Army of Karelia could not resume its advance as long as the 163rd German Division had failed to take Suvilakhti. The OKH thereupon proposed on August 10 that the Finns conduct an offensive towards Leningrad on the Karelian Isthmus. Mannerheim accepted this proposal.
There is little reason to believe that the Soviet forces in the Lake Suo area were capable of preventing a resumption of the offensive east of Lake Ladoga. It may be that Mannerheim, as noted by the Germans, was a pessimist and that unexpected developments, such as the inability of the 163rd German Division to eliminate Soviet resistance in its area of operations, could have influenced him more than it should.
However, two other possibilities are more likely to have affected his plans. One was his wish—and that of the government and the vast majority of the Finnish people—to recover lost territories and to incorporate areas in East Karelia. The second reason is that the performance of German units in Finland had disappointed Mannerheim and may have colored his views of the progress of Field Marshal Wilhelm Ritter von Leeb’s Army Group North. This Army Group had made rapid progress through the Baltic States mainly because Marshal Voroshilov did not intend to make a stand in those areas and had successfully withdrawn his forces virtually intact. There were no great encirclement battles as in other areas on the Soviet front. Voroshilov began to offer stiffer resistance when the Germans reached Russian territory. The countryside was unfavorable for the use of armor between Lakes Ilmen and Peipus and the advance of Army Group North slowed to a crawl. Leeb planned to begin his final push from the area west of Lake Ilmen and Hitler reinforced him with an armored corps from Army Group Center. It was this drive that the Germans wanted the Finns to support, first by an attack east of Lake Ladoga and finally by an attack towards Leningrad over the Karelian Isthmus.
After clearing out the northwest shore of Lake Ladoga, Mannerheim ordered II Corps to turn south against Pakkola, at the narrowest part of the Vuoksi River. That river was crossed north of Pakkola on August 18, and before long the Finns had a sizable bridgehead that favored both a continued advance southward and a move to the northwest to threaten Soviet forces facing IV Corps. At the same time another column on the left flank of II Corps drove southward from Kegsgolm, clearing the east shore of Lake Ladoga as they advanced.
The IV Corps began its offensive on August 22. The nine-day delay between the time II Corps was turned south and east and the launching of the attack by IV Corps made excellent military sense. Those nine days allowed II Corps to get on the flank and rear of the Soviet forces facing IV Corps. In fact, the Soviets became so unnerved by developments that they began destroying their own border fortifications on August 21. There was little resistance at the outset of the attack and the Finns reached Kilpenjoki on August 23. A northwest drive by II Corps from its bridgehead north of Pakkola got to within 12 kilometers of Viipuri.
The Soviets had three divisions in the Viipuri area. Their plans were to hold the city with one division while the other two launched a drive against Pakkola to eliminate the Finnish bridgehead over the Vuoksi River. It was planned that a division coming from Kilpola Island to the northeast would join them in the Pakkola attack.
The Finns acted so rapidly that the Soviets were unable to put their plan into operation. The city of Viipuri was quickly encircled. The 12th Finnish Division under Colonel Einar Vihma advanced southwards along the right bank of the Vuoksi River and made contact on August 22 with the 18th Division from II Corps, coming from the southeast from the bridgehead north of Pakkola. This put the whole right bank of the Vuoksi River in Finnish hands.
The Soviets launched a counterattack with two divisions—123rd and 115th—against the Finnish forces east of Viipuri on August 24. They managed to push the Finns back about five kilometers without breaching the front. The Soviet forces were pushed back to their starting positions the following day when the Finnish 26th Infantry Regiment from the 12th Division was committed. On the same day that division succeeded in cutting the railroad between Viipuri and Leningrad.
The 8th Finnish Division, commanded by Colonel Winell, had been engaged in clearing operations along the western shore of the Bay of Viipuri in preparation for crossing that bay. The crossing of the bay to Lihaniemi Peninsula began on August 24 with the 3rd Battalion of the 45th Infantry Regiment leading the way. The peninsula was secured by the end of the day. Forces from the 8th Division expanded their beachhead the following day and cut the railroad from Viipuri to Primorsk running along the shore of the Gulf of Finland. The 12th Finnish Division had also continued its advance. On August 27 it cut the main road from Viipuri to Leningrad, effectively sealing off Viipuri from the outside world.
The Supreme High Command of the Soviet Armed Forces (STAVKA) recognized the hopeless situation in the northwest corner of the Karelian Isthmus and permitted the 23rd Army to withdraw from Viipuri to a new defensive line near where the Mannerheim Line had been located in the Winter War. They gave up trying to defend Viipuri, which was occupied by Finnish forces on August 29. However, the withdrawing Soviet forces soon found their route of retreat to the south blocked by the 8th Finnish Division. They managed to force several convoys of trucks through before the Finns permanently closed that escape route. The retreating Soviet troops were encircled about 10 kilometers south of Sveklovichnoye (Porlampi). They defended themselves desperately and a sizable part of the force—about 12,000 men—managed to break through the western encirclement force and escape to Koivisto Island after abandoning most of their vehicles and equipment. They remained on that island until they were evacuated in November. The remaining Soviet forces in the encirclement were cleared out by the Finns on September 1. At least 9,000 surrendered to the Finns and over 7,000 were killed in the fighting. A large amount of equipment was captured, including 306 artillery pieces, 55 tanks, 673 trucks, and approximately 4,500 horses.