Pressure working in submarines

Answer 1

"Pressure in the Boat", as it is called, is maintained by increasing O2 and environmental pressure levels throughout the boat. Keeping pressure in the boat is a major safety factor; any significant breach in the hull, a valve, hatch, etc., will be seen by the Chief of the Watch as a drop in internal pressure. While major flooding is readily apparent, small leaks might not be, and when underwater at any significant depth you don't want to give sea pressure any chance to make a small leak a large flood. If you're wondering how to tell the difference, if it's a leak, you'll find it; if it's flooding, it'll find you.

Air Pressure is also affected by hull compression as a boat goes deeper, though being isolated inside the pressure hull, the crew hardly notices any change in pressure at all. In fact, the only way to know you're ascending or going deep is if you're facing forward or aft and walking up or down on an angle, or if you're sleeping, your sleeping on your head or on your feet. Normal operations running at specific depths feels like sitting in your living room - you actually feel more driving in your car.

Of course depth changes can be made without any angle (0 bubble), in which case the biggest indicator to the crew is the noise of hull popping, the noise made by the hull as it compresses/decompresses with the changes in sea pressure.

If a boat has been submerged for a good period, the initial opening of a hatch when surfaced must be done slowly and deliberately. Before the danger was known, in older submarines, unsuspecting crew were literally blown out of a hatch if the pressure was high enough; today's modern hatches have a strong safety latch to prevent the hatch from being blown open by pressure if the person opening the hatch opens it a bit too quickly. They can still be injured though; the pressure can be strong enough to push a large man into the hatch, causing severe injury.

The air in the boat is typically equalized with outer air by ventilating through the boat's snorkel mast. However, not all tactical situations allow for this, hence the problems and precautions I've described above.

If you're referring to Mental Pressure - absolutely, 24/7/365. But all submariners thrive in pressure situations (a requirement for being Qualified in Submarines), so it's not a problem.