[Dron22]

I completed the previous mission with all extra objectives, I think it's supposed to affect certain things in Ocean Vulture, such your starting position.
When I started the mission, the enemy surface ships were sailing towards me from the east, while my sub was heading at bearing 0, straight North to intercept them. After I completed the main objective, I headed East towards the exit area and where the 3 Russian subs are. When I attacked the Russian subs, the surface group was already gone West. I sank the Akula II and Kilo with active homing torpedoes, I tried active and passive on the Victor III pointing them manually directly at it and enable them when there are no counter measures nearby. The torpedoes just pass the Victor III by a few meters and miss it.
Update: After several more attempts at sinking that Victor III sub in Ocean Vulture, I decided to leave that Victor III alone and complete the mission. I now got to Escort SAG mission, where I encountered two Victor III subs and sunk them without any trouble. I am now almost sure that it's bug in the Ocean Vulture mission.
If you have the time, play the Ocean Vulture mission as a Seawolf US sub and see if you can sink the Victor III.