The 'Petrozavodsk, Ukhinskom-Rgozerskom and Olonetskom Defensive Operation' was a Soviet fourth sub-operation of the 'Arctic-Karelia Strategic Defensive Operation', and as such the Soviet response to an element of the Finnish and German 'Polarfuchs' (i) (1 July/10 October 1941).

The spur for this Soviet undertaking was the Finnish invasion of East Karelia as part of the first stage of the latter’s 'Jatkosota' continuation war in the summer and autumn of 1941. As a result of this most southerly component of the German and Finnish three-element campaign in eastern Finland, the Finns occupied East Karelia and held it until 1944. For more than one month before the outbreak of the 'Jatkosota', Kenraaliluutnantti Erik Heinrichs’s Karjalan Armeija (Army of Karelia) had been prepared for the task of recapturing the Karelian isthmus, lost to the Soviets as a result of the 'Talvisota' winter war of 1939/40. Since their seizure of the isthmus, the Soviets had built fortifications and brought additional troops into the sector.

Eversti Erkii Raappana’s Finnish 14^th Division operated under the direct command of the Finnish headquarters, and began its advance on 4 July as the northernmost Finnish unit to the south of the demarcation line between Finnish and German forces. It was opposed by elements of the 54^th Division, and encircled and savaged the defending 337^th Regiment at Omelia before maintaining its advance toward its goal of Rukajärvi and the Ontajoki river. The advance was halted by Marsalkka Carl Gustaf Emil Mannerheim, the Finnish commander-in-chief, on 17 September after the 14^th Division had attained its goals.

While the earlier offensive in Ladoga Karelia, to the north-west and north-east of Lake Ladoga between the Karelian isthmus to the south-west and East Karelia to the north-east, by Kenraalimajuri Paavo Talvela’s VI Corps of the of the Karjalan Armeija had been successful, the same was not true of all Finnish offensive undertakings. The advance of Kenraalimajuri Woldemar Oinonen’s 'Oinonen' Ryhmä (otherwise the 'O' Ryhmä) had become bogged down almost immediately, and Kenraalimajuri Woldemar Hägglund’s VII Corps had been completely occupied in clearing the encircled Soviet forces from the Sortavala area. While the Finnish command had halted the offensive, this did not prevent local commanders from preparing for further attacks. This meant the repair of roads and railways leading to the front lines. The left flank of the Karjalan Armeija also received authorisation to capture tactical start positions.

The 'Oinonen' Ryhmä and Eversti Kaarlo Heiskanen’s 11^th Division of the VII Corps were ordered to capture the area of Suvilahti and Suojärvi. The attack was launched on August 19 and forced the 71^st Division to withdraw by 21 August. The Finns pressed on and captured the village of Tsalkki and its important crossroads on 23 August. The exertion of steadily increasing pressure allowed the Finns to advance and reach the eastern shore of the Säämäjärvi lake on 1 September.

In the Finnish plan for the offensive that was to begin on 4 September, the VI Corps was to advance from its current positions near Lake Ladoga to the south-east and reach the Svir river, while the VII Corps was first to take the important crossroads of Prääsä and then continue to Petrozavodsk. This offensive was believed to be much more difficult than the previous Finnish offensives because of the relatively unfamiliar terrain, the width of the front and the expectation that Soviet reinforcements would be sent to protect the Murmansk railway passing through this area.

The Finnish forces comprised formations and units of the Karjalan Armeija. Farthest to the south was the VI Corps with two divisions (Eversti Ilmari Karhu 5^th Division and Eversti Aarne Snellman’s 17^th Division) in front line positions and Eversti Ruben Lagus’s 'L' Ryhmä, the latter comprising Lagus’s own 1^st Jäger Brigade and elements of the 5^th Division, as the mobile reserve. In the centre, the Finns deployed the VII Corps with an initial establishment of two divisions (Eversti Paavo Paalu’s 1^st Division and Eversti Kaarlo Heiskanen’s 11^th Division) soon reinforced by Eversti Antero Svensson’s 7^th Division. Farther to the north, the Finnish deployment was based on the 'O' Ryhmä and Generalleutnant Erwin Engelbrecht’s German 163^rd Division. Farthest to the north was Everstiluutnantti Eero Kuussaari’s 'K' Ryhmä of approximately brigade size.

The Soviet forces comprised General Leytenant Filipp D. Gorelenko’s 7^th Army, which had been divided into the 'Olonets' Operational Group located to the south and the 'Petrozavodsk' Operational Group in the centre. The 'Olonets' Operational Group consisted of the recently formed 3^rd Militia Division, with the 3^rd Naval Brigade held in reserve, but was soon reinforced with the 314^th Division. The 'Petrozavodsk' Operational Group consisted of the 272^nd Division, with the 313^th Division in reserve. The 71^st Division defended the area farther to the north.

The Finnish offensive started early on 4 September at Tuloksa, when the Finns unleashed their largest artillery barrage of the war up to this time. The 5^th Division quickly broke through the Soviet defences and crossed the Tuloksa river. Once engineers had hastily built a pontoon bridge, the mechanised 'L' Group Ryhmä headed at speed to the east. Comprising the 3^rd Marine Brigade and supporting infantry regiments, the Soviet defenders were forced to retreat or otherwise were encircled by the advancing Finnish forces. The 'L' Ryhmä used its mobility to advantage and captured Olonets on 5 September. Soviet attempts to re-form for the defence were hindered by the fact that most of their forces now consisted only of units which had been broken.

The 5^th Division and 17^th Division were also committed to the Finnish offensive, and began with an advance toward the village of Nurmoila, which was held by the 3^rd Militia Division. Attacking from both the south and the north, the Finns forced the defending Soviets to withdraw to the east despite the field fortifications which the Soviets had constructed to the area. However, the Soviet withdrawal prevented the Finns from closing the pincer they had planned to trap the Soviets, and on 7 September a strong infantry contingent together with the headquarters of the 3^rd Militia Division managed to escape along forest paths, though the escapees had to abandon their heavy weapons and equipment.

The advance of the 'L' Ryhmä reached the Svir river on 7 September 7 near the town of Lodeynoye Pole. On the same day, a detachment of the 17^th Division cut the Murmansk railway. The Finns pressed on and captured the railway bridge over the Svir river at Svirstroy on 13 September. By 22 September, the VI Corps had advanced to the south of the Svir river, in the process capturing Podporozhye and then adopting defensive positions. The Finnish bridgehead was at this point about 25 miles (40 km) wide and between 3.1 and 6.2 miles (5 and 10 km) deep. The 5^th Division took up positions on the northern bank of the Svir river as far as this waterway’s mouth, while the 17^th Division occupied the bridgehead in the area to the south of the Svir river.

The advance of the 11^th Division toward Pryazha (Prääsä in Finnish) encountered strong resistance but was able to advance through the forests and encircle the defending Soviets. The advance was slow, however, and it was only on 5 September that the road leading to Petrozavodsk was cut by the Finns. Encircled Soviet units made several counterattacks against the Finnish roadblock but failed to clear it. The steadily advancing 11^th Division captured Pryazha on 8 September. Meanwhile, the 1^st Division closed on the village of Pyhäjärvi directly to the south of Pryazha. By 16 September the 1^st Division had reached the southern end of Pyhäjärvi while the 7^th Division had passed round the flank of the defending Soviet forces and reached positions to their rear. After suffering heavy casualties, the surrounded Soviet forces escaped through the forest after abandoning their heavy equipment. The 11^th Division continued its advance first to Polovina on 24 September and from there to the crossroads at Vilga, a mere 3.75 miles (6 km) from the suburbs of Petrozavodsk, on 28 September.

The Soviets had appreciated at an early stage that all attempts to hold Petrozavodsk against the Finns advancing from both the west and the south would by costly. In an attempt to do bolter their first-line strength, the Soviets formed several new formations from NKVD (internal security) units, broken-up or separated army units, and reinforcements. These new elements included 37^th Division and the 1^st Light Infantry Brigade.

The Finns also brought in reinforcements in the form of Eversti Kaarlo Viljanen’s 4^th Division, which was despatched to advance along the road leading from the Syamozero lake toward Petrozavodsk. By 14 September the division had already met fierce Soviet resistance, but the numerically superior Finnish forces managed to encircle and defeat the defending 313^th Division, which was forced to retreat after suffering heavy casualties. The clearance of the last of the mottis (groups of encircled Soviet troops) took until 26 September. Elements of the 4^th Division continued their advance with the object of cutting the road to the north from the Petrozavodsk. The Finns captured the village of Markkila on 19 September, but in several attempts failed to breach the 313^th Division’s defence at Besovets (Viitanain in Finnish). While the 4^th Division was unable to complete its task of cutting off the Soviet forces defending the area of Petrozavodsk, it did pin a considerable number of Soviet troops and protect the only vulnerable flank of the Finnish advance.

Meanwhile, the 'L' Ryhmä had been advancing to the north-east from the Svir river, but its progress was somewhat slower than had been expected as a result of heavy autumn rains that turned roads into morasses. By September the advance had reached the village of Ladva, where the 'L' Ryhmä met the 7^th Division and together the Finnish units encircled and then defeated the defending 3^rd Militia Division. Elements of the 'L' Ryhmä pressed on and reached the shore of Lake Onega on 23 September, and thereby cut the route to the south from Petrozavodsk.

The Finnish advance had pressed the defending Soviets into a small area in the vicinity of Petrozavodsk, and only the efforts of the 313^th Division kept open the sole remaining land route. The advance of the 11^th Division reached the town on 1 October, but this Finnish formation could not close the escape route until the following day. Meanwhile, the 1^st Division, which had been clearing mottis near Pryazha, now reached the front and captured the town later on the same day. The modest speed of the Finnish advance had, however, made it possible for several Soviet units to escape from the encirclement. The fall of Petrozavodsk also broke the resistance in the south, the direction from which the 'L' Ryhmä had been approaching the town. The 4^th Division also finally broke through the Soviet defences at Besovets, and this left Petrozavodsk firmly in the hands of the Finns, who renamed the town as Äänislinna.

While most of the Finnish forces in the area had been focussed on the capture of Petrozavodsk, elements of the 7^th Division had advanced along the shore of Lake Onega to the mouth of the Svir river. Attempts to cross the river on 6 October failed as a result of fatigue and the men’s initial refusal to attempt the crossing, but the attempt on the following day in bright daylight was successful. The rest of the division followed once the bridgehead had been established. This made it possible for the new bridgehead to be merged with that created earlier in the offensive. A Finnish attempt to gain ideal defensive ground came to an end at Oshta when the Finns encountered the fresh 114^th Division. Neither side could gain any advantage in the fighting that followed, and the Finnish forces started to prepare for defence in the bridgehead to the south of the Svir river, which was enlarged to a width of 62 miles (100 km) and depth of 12.5 miles (20 km).

The seizure of the town of Medvezhyegorsk (Karhumäki in Finnish) was set the goal for the continued Finnish offensive. Troops advancing from various directions towards the town were grouped as Kenraalimajuri Taavetti Laatikainen’s II Corps, which thus comprised the 4^th Division, 'O' Ryhmä and 'K' Ryhmä and was reinforced with Eversti Claes Winell’s 8^th Division transferred from the Karelian isthmus. Opposing them was the Soviet operative group comprising the 37^th, 71^st and 313^th Divisions, all of which were well below strength. The Finns advanced along two routes: a larger group following the road from Petrozavodsk toward Medvezhyegorsk; and a smaller group followed the road from Porosozero (Porajärvi in Finnish) toward Paatene at south-western end of the Segozero lake.

After advancing to Paatene, the Finns were able to establish communications with the 14^th Division, which had earlier reached Rugozero. Medvezhyegorsk was captured on 5 December in a three-pronged attack, and by the following day the Finnish spearhead hd taken the town of Poventsa (Povenets in Finish). After this, the Soviets destroyed the locks of the Stalin Canal on 8 December, and this immediately caused the flooding of Povenets, though the damage was largely superficial.

Mannerheim had earlier ordered that the Finnish advance would end on the line linking Povenets and the Segozero lake, so the capture of Povenets ended the Finnish offensive.