Vixen
Penultimate Amazing
We don't know the system didn't pick up the sub. You made that bit up.
NATO held a similar exercise in 1993 and a secondhand Russian submarine was sneaked out then, undetected and only picked up later by equipment at Bornholm Island - some 500 miles away from St Petersburg. The disclosure led the USA to formally complain about Russia selling equipment to countries like Iran and other tin-pot Third World dictatorships. Iran had a contract for more Russian submarines. The point being made here is that there was a massive convergence of NATO ships and aircrafts in the region, they never spotted the acoustic signatures so Russia knew that a NATO exercise was a good time to 'go under the radar' as it were in its hostile activities. The inference to be drawn is that were there a Russian submarine within the vicinity of the Estonia one could be none the wiser, due to the large presence of NATO submarines all over the place.