Some of the most speculative (but with little to no support) seem to think they were carrying a cobalt nuke larger than the Tsar Bomba.
basically a series of interconnected bathyspheres with a hydrodynamic shell over them.
http://www.hisutton.com/images/Ru_Losharik_Cutaway.jpg
Skegs, hydraulic manipulator, no weapons. It's clearly ment to tamper with undersea cables.
I agree that tampering with cables seems like the obvious reason for the military to go super-deep. With recovering sunken things made by your adversary a close second. And in the mid-1980s, they were much better at titanium than at video cameras.
Submarine itself looks cigar shape, but that is just her outer shell, it's pretty certain that outer shell is not pressure sealed but rather that internal spheres withstand the pressure while the just the shell around it.
Fire drill is like a number 1 drill in the fleet, and a submariner, moreover a captain should be able to do it with his eyes closed
An old friend of mine has recently finished his term in the Russian military. According to his words explaining his own experience, and things he heard during military exercises from guys from other parts of the country, most soldiers are being trained not to defend their country, but to do three things: paint walls, wash their clothes, and clean up the premises.
It's no wonder you can mistake a passenger airplane for a military aircraft after such a stimulating experience.
https://en.wikipedia.org/wiki/Iran_Air_Flight_655#Post-tour_...
MH17 was shut down because the radar operator could not read his screen / correlate with other sources of information regarding civilian flights. Can tell you a bit about how professional those operators were.