11,000 miles (18,000 kilometers)
To put that into perspective, the circumference of the earth is ~24,000 miles. From my rough Google Earth calculations, the stated range covers the entire planet except for a tiny sliver of Antarctica and a bit of the ocean nearby.
Why would Russia need a missile with that range? Unless they just really want to take out New Zealand first, it kinda seems like they just picked the largest sensible range value (12,000 miles, halfway around the planet) and then fudged it down a bit because why would you need to fire a missile more than halfway around the planet? Just fire it in the opposite direction.
Nah if you only build a 2D structure, you won’t have to worry about the water pressure because your structure will likely not be able to interact with 3D matter. It’s genius engineering IMHO.