It only takes a little over a minute to walk 100m. And if I stand at point A and look at point B, 100m away, it doesn’t feel far away either.

That’s why I think even though I am only able to swim what 4 meters or something down, maybe less, 100m under the water sounds really little for a submarine. Also probably because I have no experience with submarines so I was imagining that for the most part they would be many hundred meters under the sea level.