My last speculation for tonight- how could there have been during WWII a largescale naval battle between the Soviet navy & either the Germans (pos during the siege of Sevastopol, Leningrad or another major port city in 1941/42) or the IJN (poss towards the end of 1945, in support of Op EASTERN STORM & the invasion of the Kuriles- if the Japs still somehow had enough capital ships to put up some fight) ? Who would win ?
Soviet Navy at the time of WWII consisted of two battleships in the Baltic and one battleship in the Black Sea, all three of them were extremely outdated, so possibility of Soviet active naval operations is close to zero.
German Navy (one battleship and two battlecruisers) could enter Soviet waters in the Baltic and try to destroy the USSR's Navy, but there was absolutely no need for such risky actions - Luftwaffe successfully bombed Soviet bases, sinking battleship
Marat and crippling her sistership
October Revolution. With Germans dominating air, possible outcome of Kriegsmarine's raid into Gulf of Finland would be the same or even worse for the Soviet Baltic Fleet (Germany would probably lose some minor units on minefields and seriously damage their capital ships).
In the Black Sea Germans could appear only after cruise around Europe and through the Turkish Straits. Such expedition could become possible only with British noninterference and Turkish help - both events being highly unlikely. Italian Navy in the Black Sea would be somewhat more plausible, but still almost impossible in the OTL WWII. Maybe, in the ATL where Hitler occupied Stambul, but gave up African campaign, Italian attack on Sevastopol could be real. In such case
Paris Commune (only Soviet capital ship in the Black Sea) would most likely remain in Poti (relatively safe base far from front). If she would be ordered, nonetheless, to go to defense of Sevastopol in spite of Italian threat - outcome would be very unpleasant for the Soviet Navy. Under
Littorio-class battleships' fire and constant Luftwaffe's attacks Soviet ships would sink soon after nearing Crimean coast.
Regarding plausibility of Battle for the Kuriles in 1945 with Soviet Pacific Fleet and IJN as participants - first of all, the Japanese had not fuel for their ships in April 1945 already, so in August 1945 any remaining IJN units would be at best floating batteries. Secondly, Soviet Air Force dominated skies over Kuriles even more completely than Luftwaffe dominated Crimean air in 1942. Consequently, even with miraculously supplied fuel
Nagato or
Katsuragi would be destroyed by the Soviet planes long before their appearance near Soviet landings' sites. If somehow some Japanese ships would reach the Kuriles, they would have slim chances to sink several Soviet cruisers before sinking themselves (full-scale naval battle would still be impossible - Soviet Navy had not capital ships in the Pacific before 1980-ies, and transfer of obsolete battleships from the Baltic or Black Sea fleets would be unreasonable).