Just had my first ever submarine experience. How did they communicate with the world?

[Dallsim]

After joining the forum, I decided I mind as well learn a thing or two about submarines.

Strangely enough, my first ever experience in a submarine just happened to happen this weekend while I was on holiday in Hamburg, Germany. They had a Russian submarine (U-434 or B-515 in Russian) docked at the port, which was now open and used as a museum (since 2002) for the general public.

My girlfriend is very much into history (pre and post world war) and luckily mentioned the fact that there was a submarine open for visitors in the city. She was surprised to learn that I immediately showed such interest in visiting and I am happy we made the choice to go

Unfortunately, they did not seem to have a guided tour in English so I had to rely on my secondary school German skills for most of the tour, which was held in German. My girlfriend speaks the language fluently so I was able to ask a FEW questions after the visit but obviously wonder about a lot more things and hope to get some clarifications from other subsims' forum users if possible.

What I learnt during the tour:

The submarine, or U-Boot as it is called in German, was approx. meters long and 15 meters tall. It could go down to 400 meters maximum and would collapse at 600m. The crew would consist of 84 marine soldiers all together and the submarine would have to come up for air every 3 days. They were mostly at sea for 3-5 months depending on the mission. It was diesel driven mostly around surface but switched to batteries when going deep. Temperatures were 40 degrees Celsius and further 60 degrees in the engine room, which shocked me like crazy! Also, when enemies or perhaps other boats would pass by, they had to switch off the engine and remain completely silent, thus having to turn on the heaters to stay warm. Otherwise they would freeze to death!

Everyone worked 12 hours a day and would sleep or relax for the other 12. There was very little space to move around in, and my recent slight knee and hip injury made it extra difficult to get around. The ideal height for a person would be 160cm, making it quite straining on the back if you were taller. The submarine innards were clearly not made for esthetics but rather function. The rooms were small and the beds were short. The only room with proper space and bed size seemed to be the "panic room", most probably for good reason.

What I definitely took an interest in was with outside communication but do not think too much was explained. How did the submarine communicate with the outside world? On top of the submarine, you could see communication tools in the front section of the sail, like a satellite of some sorts with two periscopes to the back. How was communication between the Russians done securely without it being intercepted or modified? What was the technology like back then compared to now? Are there still any similarities? My girlfriend claimed it was possible to hear speaking "sounds"
coming from a submarine if you were above sea level. Is this actually true?
Man, I have too many questions

My girlfriend had not heard of the film "Das Boot" so we will watch this once we're back in the country. Also, "the Hunt for the Red October" should be next on the list. She had at least heard of that one.

http://www.u-434.de/index.php (German only)
https://en.wikipedia.org/wiki/Soviet_submarine_B-515