B515 is a Tango diesel electric submarine, so she would be rather quiet, if I recall probably one of the quietest diesel boats the Soviets had until the Kilos.
So...communication. IIRC generally speaking orders would be sent at specific times during the day during which time the submarine would either put up a mast if the coast was clear, or stream a wire if it wasn't. A small line of wire is not that easy to pick up on radar and unless you're pretty much on top of it it's also harder to see than a mast which leaves a trail.
That being said, in certain waters, such as the Pacific, if you're that close to the surface then a passing helicopter might actually be able to see the submarine in the clear water, not exactly ideal, so if a helicopter was detected by the submarine then chances are it would just avoid being near the surface wherever possible or spend as little time up there as possible.
Let's also bear in mind detection, radar is generally done through a series of sweeps and radar returns can be made off all kinds of rubbish in the sea, so if a submarine sticks up a scope and a ship gets no more than two returns off it, the radar operator may classify the returns as ocean clutter, which is when the radar reflects off something random on the sea, like a flock of birds or something. So a quick sub commander can get a mast up, do a sweep and slam it back down again before the surface radar operator gets a solid lock and determines that it's a mast out there. That's one of the reasons that submarines like the Astute and Virginia classes have periscopes that are essentially a load of video cameras around a pole, you can pop it up, grab the footage you need, drop it down again and then analyse the footage you've got without having to leave the mast up or suffering motion blur as you turn the scope around quickly.
There is another method, and that's ELF (Extremely Low Frequency), and this is mainly used for missile submarines in order to tell them to come up to periscope or wire streaming depth in order to receive a more detailed message, since ELF has a very slow transmission time and as such is really only suited for short messages. If you've seen the film 'Crimson Tide', you'll see that they get an ELF message to bring them up to communications depth in order to receive missile targetting instructions.
And, of course, there's the underwater telephone for communication between submarines. IIRC the nickname for it is the Gertrude and it's pretty primative and often a bit like trying to have a conservation on a very bad phone line, but it does work.
In the future, there's a lot of talk about laser based communications, a bit like fiber optics but through the water rather than a fibre tube. The precise physics of it are a bit beyond me, but I do know that laser comms on submarines is something that has been mulled over for a while now and it wouldn't surprise me if it is in actual service but on a classified trial basis.
I hope that makes sense...and that any sub experts can correct me where I've gone wrong, I'm certainly no expert but I have read a bit over the years, especially around Cold War submarines (my favourite era) and so I've picked up the odd thing here and there. There's some articles I'll link as well for some extra reading:
https://en.wikipedia.org/wiki/Commun...ith_submarines
https://en.wikipedia.org/wiki/Underwater_telephone
http://www.sea-technology.com/featur...munication.php
http://www.naval-technology.com/feat...quantum-level/