Since it seems to be about the time might be worth posting this.
TLDR… Soviets sent over 600 strong raiding unit into the Finnish rear in late summer of 1942. The unit suffered from horrible supply situation, was hit very hard by the Finns, and failed to reach its intended targets with only around 120 of those taking part managing to return. Finnish losses (altogether) were 119 men.
First a bit of background…
After the Finns stopped their offensive late in the 1941 the work on more static defenses began. This resulted in complex network of trenches on both sides. However this only applied in some of the sections of the front. On other sections of the front there were only patrol routes and outposts (or firebases depending on how you want to call them). So it should be no surprise that there were long range patrols sometimes very deep in the opposing side’s territory. The Finns had launched several quite successful long range patrols to hit Soviet targets far beyond the front lines in 1942. These targeted the mostly the Murmansk rail - especially notable were the raids at the supply depot and railroad station of Maj Guba (Mayguba) and at the supply depot of Petrovski Jam. The latter raid is a matter of some controversy as the raid launched during midnight in February did also hit a military hospital which was part of the supply depot (though based on records the Finns didn’t know that there was a hospital in there).
So… The Soviets decided to start their similar raiding actions which were in this area for some reason dubbed as ‘partisan operations’. Then again there were very limited if any ‘traditional’ partisan activity and most of the partisans were in a way raiding parties in this area. The Finnish opinion towards these varied a lot, those which acted like military units were treated as such (including POW status) however those which did not were considered essentially as illegal combatants - and treated accordingly. In 1942 when the lake Onega was still in strong ice there had been across the ice raids there. Of the Soviet raids perhaps the most notable was the raid in the peninsula in the northern end of lake Onega.
Actual operation…
In July 1942 the Soviet Partisan Brigade (known variably as the “1st Partisan Brigade”, “Pudozh Partisan Brigade”, “Grigorjev’s Partisan Brigade” - referred to as PB from here on) started its operation to penetrate through the Finnish patrol lines and raid the Finnish HQs and supply bases located at Kondopoga (Kontupohja) and Porosozero (Porajärvi). Strength of the unit when it crossed the Finnish patrol lines was 638 men and women. Plan had been to penetrate the Finnish lines in a rapid march towards west and then turn south towards the targets. Unit’s penetration of the Finnish patrol lines was detected already on 11th July and the first fighting began already then. Light Finnish units (with aerial recon units) started chasing the PB (at times having just a platoon chasing a 600 men strong unit).
The Soviet plan had relied on the rapid movement of the men (the PB was explicitly trained for such operations) with light equipment while additional supplies were to be airdropped. The problem was that the initial airdrops failed and the unit started facing severe lice problems. So the PB headed to a small village (logging camp) of Tumba where several large sauna’s were located. However before the supplies arrived the Finnish pursuers arrived as well as and forced the PB to withdraw. One prisoner was captured by the Finns who didn’t initially believe that the unit would have been nearly 700 strong. At this point the Finnish HQ started assigning more troops to the operation.
The supply situation of the Soviets was dire. That the communications gear they carried was not fully reliable didn’t help either. Most of the time the PB could not reach the HQ nor did it have any means of communicating with the aircraft dropping the supplies. There were plenty of supplies airdropped but often PB didn’t find them or the Finns (who used signals intelligence units) had located them before the Soviets. Also airdropping supplies was still something fairly new to the Soviets and a number of dropped containers shattered when they hit the ground. In practice the unit relied on mushrooms and berries. On 28th of July the commander of the unit finally got a contact with the HQ and got the permission with retreat. The Finns had kept close track of the unit and knew where it was when it stopped on 30th of July to wait for supplies. That was when the Finns launched their attack.
The encirclement had not been complete and bulk of the PB managed to escape with the Finns in pursuit with many engagements being fought between the Finnish advance units and the PB. The Finns found from the area the bodies of 113 partisans including the unit commander (major Grigorjev). At this stage the unit was desperate and the pursuing Finns found signs of men starved to death, of cannibalism, and that those wounded who could not walk being abandoned to the wilderness. All the time the PB headed back northwards with the Finns making trying to stop them.
The remains of the PB still moved at rapid pace and on 15th of August run into a camp of a Finnish company took anything edible with them. The Finns were surprised of this as they had not expected the PB to have reached that far yet. The pursuit was slow as the wounded of the PB first kept suppressing the Finns and then shot themselves. This allowed the PB to reach a lake at edge of the ‘no-mans-land’ and then cross it while under fire from the Finns. Only 120 of those who started the operation managed to return and reach the Soviet patrol lines.
On the Finnish side the operation involved fairly sizable amount of forces (almost two battalions worth - though without any heavy equipment). The Finns relied heavily on radios to coordinate their operations. The terrain was densely forested (non forested patches were swamps or lakes), roadless and mostly even trackless - most of the maps were only done according to high altitude aerial photographs and their useful on the ground level as dubious. The Finns also relied heavily on airdropped supplies as no other reliable means existed. The wounded were evacuated using floatplanes and the many lakes located in the area. Fokker C X planes were used for both recon as well as dive-bombing at nighttime (i.e. aiming at campfires). The communications were also a problem on the Finnish side with at least in one instance resulting in Finnish dive bombers attacking a Finnish camp. Finnish losses from the operation altogether were 119 men.
What followed…
The Soviets never again tried a partisan or raiding operation of that scale. Largest units used afterwards were 100 strong. The Soviets did claim that the operation spoiled the planned Finnish advances intended for 1942 but in reality no plans of advancing existed. The Finns did notice issues with their response but considered the operation from the Finnish side having been a success. It is worth noting that the PB (at least in this operation) was a fully uniformed unit using Red Army uniforms and was in general considered to consist of lawful combatants by the Finns.
There are several books about this operation (some dramatized, some purely factual). Some of the older ones:
Dmitri Gusarov - Za tšertoi miloserdija , 1977 - translated to Finnish: Korpi ei tunne armoa ~ Wilderness knows no mercy
Pentti H Tikkanen - Sissiprikaatin tuho, 1973 ~ Destruction of the Sissi Brigade (Sissi ~ commando, ranger, partisan, guerilla - all depending on context)