Actually it was the other way.
Accordng to Suomen Ilmavoimien Historia vol.24, a 200kg depth charge (set to explode at 20m) was dropped 20m behind the sub periscope. Then came the oil.
How it was actually you don't know
[the same for me].
According to my sources [the list see somewhere above] - M-95 went to position from Is. Lavansaari 14.06.1942 [23.43] to Western Gogland reach. There were no radiomessages from the submarine. In the morning 15.06.1942 the large explosion was detected by Finnish [Gogland] and Soviet [Lavansaari, patrol boats] observation posts 4 miles NE from South-Gogland lighthouse [mine field "Rukajarvi"], and 16.06.1942 Finnish aircraft bombed oil spot there. 14 men were lost. So M-95 exploded/sank on sea mine or was heavily damaged by that mine explosion [and sank next day by Finnish bomber]. This description of event seems to be a little bit more correct than yours, but I would say that the ways are quite similar
Four days from the week at bottom of the sea, yes.
Four days waiting [at bottom and in surface, probable], other three days - on the way to the corresponding point. IIRC I provide you with timetable already.
M-97 exploded on sea mine 04-11.09.1942 and was detected by Finnish observation posts 04.09.1942
Shirokorad gives the following info: 01.09.1942 M-97 moved to Eastern Cogland reach and began to cross Gogland line at underwater position. There were no any radiomessages about crossing of Gogland line. Probably, M-97 exploded on mine there between 02.-25.09.1942.
Taras mentiones the following: M-97 exploded on German mine in the Gulf of Finland SW off Porkkala-Ud, 11.09.1942. Found and investigated by Swedish divers in 1990.
as the best and most detailed source in my opinion: 01.09.1942 M-97 was escorted by base mine-sweeper to Eastern Gogland reach, submarine was in diving point at 00.31. M-97 should reach the position No. 9 after that [between Helsinki and Tallinn]. M-97 didn't returned to base and there were no radiomessages from it. 02.09.1942 Finnish radiostation [in Kotka] reported [01.45] about the detection of Soviet submarine 13.5 miles NW of Is. Rodsher. 03.09. [20.45] and 04.09. [22.25] Soviet submarine base tried to communicate with M-97 but there was no answer. In the morning 04.09.1942 Finnish observation post near lighthouse Porkkalan-Kallboda detected Soviet submarine, 10.09 [23.25] Helsinki radiostation mentioned detection of Soviet submarine in that region. Probably, exploded on mine [mine field "Nashorn"], several researches mention the date of explosion - morning 11.09.1942; 20 men were lost. In 1990 it was detected S to Helsinki [59.50'/24.30'].
There were two subs at the region, of both of Iku-Turso fought, sinking the ShCh-320.
There was also Shch-308 not far away
I've already mention that this is not true [most probably] and Finns mistaked
But you still spread here even more incorrect info trying to cut corners - already two subs appeared of both of Iku-Turso fought
The same time and with the same amount of 20mm shells [IIRC ~50] Iku-Turso met with two submarines, probably
Finns claimed that they torpedoed Shch-320 but that was Shch-307 which avoided torpedo and dived, returning to the base successfully [Finnish sources are quite correct till the moment when Iku-Turso fired a torpedo....Gun fire flash blinded Finnish submariners most probably, but they thought that was torpedo explosion, Shch-307 dived at that moment].
Also to where the back line of 10th October 1942 at the Russian estimations about the sinking date of the ShCh-320 is based at?
Any answers to that question?
So what, if I don't know the answer [and nobody knows in this case] that means that "Iku-Turso" could torpedoed submarine according to your and old Soviet version?
Noch einmal for Juha who believes to his incorrect in this case Finnish sources
[hard translations especially for him
, sorry for possible transliteration errors]
Shch-320 - 1.10.1942 [19.55] went to Is. Lavansaari [escorted by base mine-sweepers No. 210, 211, 217, 218 and 3 patrol boats]. 2.10.1942 [03.30] escort ships anchored because of strong fog and the submarine went farther alone. [04.06] it reached the diving point 6 miles to the W from Is. Lavansaari and began the run to the area SW from Is. Bornholm [position No. 1 to the south of 55th parallel]. Shch-320 didn't send any radiomessages about finish of crossing of Gulf of Finland and about arrival to position No. 1; there were no any replies from submarine according to requests from the base [08.10 and 09.10]. Most probable reasons of loss - explosion on mine field "Juminda" during battery charging [it was planned to cross Gulf of Finland along the south seashore] or explosion on mine field "Seeigel" or "Nashorn". Shch-303 detected also several depth charges explosions [from German warships] in the area, evening 03.10 off Gogland. Several sources mention the explosion on drifting mine 03.10.1942 [NW off Is. Vaindlo] (where it should charge the batteries) as the reason of loss. 39 men were lost.
Shch-308 - 15.09.1942 [20.33] - 16.09.1942 [04.00] went to Is. Lavansaari [escorted by base mine-sweepers No. 207, 211, 215, 217, 218 and 2 patrol boats]. The convoy was shelled by Finnish coastal artillery from fort Ino [unsuccessfully]. Two mines exploded in mine-sweeps of one mine-sweeper east to Is. Seskar. 18.09.1942 [01.25] Shch-308 reached entry of Gulf of Finland [position No. 5], escorted till diving point. 22.09.1942 - finished the crossing of Gulf of Finland and reached the position [no messages were received by HQ, nevertheless]. 28.09.1942 HQ sent the request and it was replied by submarine commander: "No targets, can I change the position" [29.09., 23.15]. The commander of base replied [30.09., 01.08]: "after achieving the success near Is. Utö move to cape Ristna [position No. 4 - BP]". 02.10.1942 - unsuccessfully attacked Finnish convoy west off Hango [transport "Vanda"]. 07.10.1942 - unsuccessfully attacked German hospital ship "Rügen", 10 miles SW from Is. Utö [15.22]. 19.10.1942 - unsuccessfully attacked German anti-submarine ship "Schiff 47" S of Is. Utö [submarine was lightly damaged during ram counterattack of Germans]. 20.10.1942 [01.22] - Shch-308 sent a radio message about possible sinking of 3 ships [16000 brt], own damages and asked to return to the base. 20.10.1942 [22.30 and 23.05] two radiomessages were sent from the base as reply - it was allowed to return to the base and was recommended how to do it [the route to avoid mine fields and patrol boats]. No more radiomessages were received from submarine [no messages about leaving the position and beginning to cross the Gulf of Finland]. Possible reasons of loss: explosion on mine from fields "Nashorn" [most probably], "Juminda" or "Seeigel"; there is also a version that Shch-308 was torpedoed by Finnish "Iku-Tursu" near strait Serda-Kvarken 26-27.10.1942 but the area of the route of Shch-308 should not be very close to that region, also it is not clear why Shch-308 stayed on position till 26-27.10 in that case as it had the order to return back 20.10.1942. 40 men were lost.
Shch-307 - 23.09.1942 [21.10] came to Norchepinga bay [position No. 11]. The submarine was escorted by base mine-sweepers No. 210, 211, 215, 217, 218 and 3 patrol boats till diving point [East Gogland reach]. Reached the point [24.09.1942, 05.29]. Reached the position near lighthouse Huvudsher [22.30]. 28.09.1942 patrolled the area near lighthouse Landsort, rejected the attack against convoy because of low depth. 30.09. Swedish submarine was detected. 01.10. [night time] - received the order from the base to go to the position No. 6 [Aland Sea], 02.10 [02.31] - sent a message that position near Is. Arnholm was reached. 02.10 [14.14] - underwater torpedo attack against convoy [3 transports, 1 mine-sweeper], 2 torpedos from 15 cables: in 2 min 2 explosions were heard , but transport "Vanda" and mine-layer "Ruotsinsalmi" were not hit. 14.25-14.52 - enemy patrol boats dropped 11 depth charges unsuccessfully. 03.10 - rejected the attack of single transport and convoy because of large heading angle. 07.10 - rejected the attack of convoy because of the same reason, the same happened 08.10. with two detected convoys.
09.10 - Shch-307 detected Finnish submarine in the surface and prepared to torpedo attack, but Finns dived.
10.10. - couldn't attack the convoy because of action of anti-submarine vessels. 11.10. [12.26] - torpedo attack against convoy [3 transports, 3 mine-sweepers, 4 patrol boats], 59.58'/19.39' [2 torpedos from 15 cables], explosion was heard but Finnish transport "Orient" and German transport "Hiddensee" were not hit. Patrol boats and aircraft dropped 7 depth charges [unsuccessfully]. 12.10. - rejected the attack against convoy because of large distance, was detected by enemy submarine [Iku-Turso?] but dived
. 13.10. - couldn't attack single transport and convoy because of action of anti-submarine vessels. 16.10. - rejected the attacks against against 2 convoys because of large distance and heading angle. 21.10.1942 - torpedo attack against convoy [15.36; 6 transports, 2 patrol ships, 2 mine-sweepers, 2 patrol boats] - 2 torpedos from 7-12 cables, but transport avoided torpedo; anti-submarine vessels didn't attack submarine. 23-24.10 - moved to the south part of the position. 26.10. [12.07.] - torpedo attack against convoy [5 transports, 4 patrol boats], 2 torpedos from 6 cables: strong explosion in 55 sec. - Finnish transport "Betty H", 2478 brt was sank [59.54'/19.36']. Warships and aircraft dropped 10 depth charges [unsuccessfully]. [15.50] - the attack against Finnish submarines "Vetehinen" and "Iku-Turso" was rejected [Soviet captain thought those were Swedish submarines].
. [20.44] - went countercourses with "Iku-Turso" [distance 20 m], Finnish submariners made near 50 shots from 20mm gun without any damages, Shch-307 unsuccessfully tried to find Finns in the dark 27.10. [01.00] unsuccessfully attacked by "Iku-Turso" [2 torpedos missed as Shch-307 detected torpedo trails and crash dived].
In the evening received the message to return to the base, 28.10. [04.10] began to cross Gulf of Finland. 31.10. - imaginary touched 2 mine anchor lines SW from cape Tüters. 01.11.1942 [10.05.] met with Soviet patrol boats, arrived to bay Norre-Kappellacht [12.46]. 06.11 [17.00] - 07.11 [00.55] went to Kronshtadt [escorted by base mine-sweepers No. 207, 210, 211, 217, 218 and 2 patrol boats].
there is a version that Shch-408 was damaged [not sank] by "Ruotsinsalmi" + VMV 6 and sank by mine-layer "Riilahti"
Do you know the source(s) of that version?
Shirokorad  - Shch-408 was detected and attacked by enemy anti-submarine forces 22.05.1943 off Is. Vaindlo during battery charging. Aviation and Finnish warships pursued the submarine during the whole day. Shch-408 was damaged, oil leaked away, accumulators were almost empty. Soviet captain decided to emerged, called for aviation help and had artillery combat with Finnish patrol boats, charging battery during 2 h. Then Shch-408 dived again and was destroyed by depth charges. Enemy warships tried to detect submarine till 24.05.1943. In my opinion not correct description.
Taras  - Shch-408 was sank by depth charges from two Finnish mine-sweapers and patrol boat VMV-6 off Is. Vaindlo, 24.05.1943.
- mentioned as one of the possible versions that Shch-408 was damaged by "Ruotsinsalmi" and VMV 6, and sank by "Riilahti" soon. This source gives also the following info: 22.05.1943 commander of Shch-408 sent two last radiomessages one by one [02.55 and 02.58] - "under attack of enemy anti-submarine vessels, have damages, have no possibility to charge battery, send aviation for support, my location - Vaindlo.....". The group of 8 I-153 and I-16 took-off from Is. Lavensaari but lost 2 aircraft and returned back, in 8 hours 10 La-5 were sent by Baltic Sea HQ [they also lost 2 aircraft and didn't have success against Finnish warships]. Only in 20 hours the significant amount of aviation was sent but it was too late.
PS. Volks, I will return back next week here, a lot of work to do and I have absolutelly no time for all things I am interested in, sorry.
PS2. Thanks to Walter! Of course, I have no possibility to check all your interesting and huge amount of info at the moment
As for Soviet submarines of WWII period, I recommend several databases [on Russian, unfortunately]:
[the short info - dates, specifications] about all warships of Soviet Navy of WWII period. I guess ~90-100% correct info depends on the subject.
- quite good database about all Soviet WWII submarines, sometimes almost 100% correct with a very detailed newest info, sometimes not correct with the info from old sources. Need to check it in addition before start to believe to the info.
- the most detailed info about all aspects
[career day by day, blue-prints, specifications] of Russian submarines from XIX c. till present. Extremelly good site, which takes into consideration and analyzes all known info about Russian submarines from native and foreign sources, site has forum inside. I guess ~98-100% correct info depends on the subject. Site is supported by St. Petersburg union of submariners. I believe to this info in the case of any doubt.
- a lot of interesting research articles inside, excellent info about modern Russian submarines but very short info about WWII submarines, so not recommended for WWII research.
- quite good site as me seems but I never use it in my searches as it was under construction and far away from full database still