Lengt to diameter ratio of a submarine is not quite an important indicator on structural integrity or any features related to that. The maximum diameter is usually dictated by either the collapse depth of the hull or construction tolerances where these are also relating to each other.
Bro, I concur with your statement regarding the MILDEN. Hull length to diameter ratio of 7:1 to 8:1 is there as a guideline. Most nuclear subs push past 10:1. It is a matter of design and construction capability.
There is however some merit in the apprehension of
@zio ’s post. But not as drastic as he puts it.
Logically, it is a fact that short, wide cylinders resist hydrostatic pressure better than long, thin ones.
Shorter frame distributes overall load more efficiently, reducing required steel thickness. Also a minimal surface area relative to internal volume reduces the overall structural steel weight.
Hence shorter hulls experience less stress from uneven wave action when operating near the surface.
Long hulls can be highly prone to buckling under deep-sea diving pressures. Long cylinders, therefore may require massive, closely spaced internal transverse stiffeners to prevent collapse during wave action and tight manoeuvres that could cause longitudinal bending, therefore straining structural welds.
Thus in the end,
hydrodynamic performance and structural integrity is a compromise of both. So when building submarines designers would take all the above in to consideration.
if you look at the Virginia class SSN ; 140metres long with a hull diameter of 10.3 metres may look like it is pushing past the limits. But the construction designers will have taken in to account all the above and more. That is why after 25 or more already built they are still building them.
Ohio Class SSBN are 170m long with a hull diameter of 13metres.
Aukus subs are 130m long with a hull diameter of 12.8 metres.
So your last sentence of ;
The maximum diameter is usually dictated by either the collapse depth of the hull or construction tolerances where these are also relating to each other is very apt.