Overview
It is what it says it is
What you need
To make a submarine all you will need is thrust, and lots of it. To get enough trust i have created my own custom engine that produces 20,000kn of thrust.
Making your submarine
To make a submarine just build a ship that is symmetrical and that looks like a sub. Now here is the important part, you need quite a few reaction wheels or lots of RCS thrusters if you want to be able to steer/not capsize.
Next you will need to have your centre of lift in front of the centre of mass, this is important because it is the reason you will be able to submerge.
Finally you will need to make your ships centre of mass close to the bottom of it, this helps prevent capsizing as well as helping you to dive.
Testing your submarine
The first challenge is getting your sub to the water, for that i reccomend: [link]
However if you decide to not use that mod you can always drive in into the water at a speed that does not exceed the crash tolerance of your weakest part which is ussually about 5m/s
Once in the water throttle her up and you are you can now cruise the seas without a care in the world.
