Because thin metals will crush under extreme depth
Submarines would need thick, strong walls because They would have to withstand the pressure of the water that would increase the deeper they go, to do this they would need stronger and thicker materials to cope with the force (This would help keep the people safe).
Because they need to be able to withstand the pressure of the seawater outside. The deeper a submarine goes - the higher the pressure gets.
All submarines have specific design limits based on their overall hull construction material and shape. In general, the smaller, more compact, and spherical a submarine is, the deeper it can go, but that's not always the case. Hull material is a big factor as well. Most submarines today are built with steel which has elastic properties, i.e., it can contract and expand with sea pressure many times without hull degradation. By contrast, a Titanium hull (e.g., a Russian ALFA) may be able to go deeper, but the properties of Titanium make it brittle when exposed to extreme pressure over time. Think of a the difference between squeezing a tennis ball repeatedly, and an egg - the egg will begin to crack well before the ball ever will.The other main reason is that at deeper depths, it doesn't take much damage to the hull to cause a major casualty. At the massive pressure of deep ocean depths, even minor damage can result in catastrophic flooding and failure. You don't need a submarine that can go to deep depths - all you need is a weapon that can go to deep depths.
When they go deep under water the pressure would increase so you would need stronger and thicker materials to cope with the force
submarines are important because people need to go under the sea and do what they got to do to save the world
Nuclear submarines are powered by a nuclear reactor and they are completely independent of air, so there is no need to surface frequently.
HY80 steel and variants, a flexible steel alloy, has for decades been used on modern U.S. and Allied submarines. Its flexible properties are what makes it an asset - it contracts and expands as sea pressure increases/decreases with submerged operations. Internal submarine decks are not actually attached to the hull - they're actually hanging from from suspended cables and the decks are several inches from the sides of the hull to allow for the contraction as the boat goes deep. About 25 years ago, there was a lot of controversy about the Russian ALFA class Fast-Attack and her known Titanium hull, able to reach depths near 3000'. Many in Congress wanted to know why the U.S. didn't have something similar. Fortunately, idiots remain in Congress and Engineers design Nuclear Submarines. Titanium is extremely strong, but it is not flexible - sure, the ALFA can dive deep, but each time it puts stress on the hull when it deep-dives it becomes more brittle over time. It's like putting increased pressure on an eggshell - eventually it'll crack. This doesn't happen with HY80. It remains flexible over decades and hundreds of dives and surfaces. Also, you don't need a submarine that can go to 3000'. All you need is a weapon that'll go to 3000'. At that depth, even minimal damage to the pressure hull would result in a major casualty and likely loss of the boat.
No - all submarines, be it nuclear or diesel-electric, use diesel fuel, either for primary engines (DE) or backup generator (nuclear).
you need sea defenses to keep unwanted vessels (boats, submarines, etc.) out.
The nearest Budget Cars is on 1 Yard Applegarth Rd which is in Hull United Kingdom. So this is within the town of Hull, no need to leave there in order to get a Budget car.
R25 can be many different thicknesses. It depends on the insulation product. Styrofoam SM would need to be 5" thick. Pink fiberglass would need to be about 7" thick. White (beadboard) styrofoam would need to be about 6.75" thick. Blown in attic insulaton would need to be about 10" thick.
Eskimos need thick boots to insulate their feet, as it is very cold where they live.