Good day good people,
I’m curious, kind of why I’m here!
Given everything else: propulsion, weapons if any,crew size etc. is there an optimal design for a very deep diving sub. I’d noticed the competitive nature of the latest Marianas Trench dive and wondered why the argumentitive Navies hadn’t gone deep as well as carrying absurdly large weapon loads.
OK, so accepting you don’t want to launch a potentialy and personaly dangerous weapon from 5 miles below, but once a pressure hull is built that it?
Is the question in the ‘etc.’
I know the USSR made Sub hulls out of Titanium and never really understood the whys and wherefores of that…
There’s not much point in creating a super deep-diving sub for military purposes. Any attack you launch is going to require you to come up near the surface anyway, which largely eliminates any advantage from diving deep. And engineering a submarine to go REALLY deep is a major technical challenge. The pressure increases by one atmosphere for every 10 meters deeper you go, so the hull has to be correspondingly thicker and heavier, which cuts down on the number of weapons you could carry.
The technology to dive to the deepest part of the ocean only came into being in the last few years. That is why there haven’t been any manned dives to the deepest parts of the ocean yet.
That’s not true; the Trieste was built nearly 60 years ago and dove to the bottom of the Challenger Deep (in the Mariana Trench). However, you’re almost certainly right that we don’t have the technology for an armed, manned, effective military sub that reaches those depths.
I don’t know any more than the wiki article says. The ship was basically a giant gasoline balloon (gasoline is lighter than water but incompressible) so that the ship could maintain positive bouyancy; it had a spherical crew capsule made from 5" thick steel dangling below it. It wasn’t very complicated, and it didn’t do much, but it did successfully transport two people to the bottom of the trench and back up again.
Unless you use a bathyscape design like the Trieste, where a large oil-filled balloon provide buoyancy, then the limit on how deep a submarine can dive is how thick it’s hull can be before it’s heavier than an equal volume of water. As alluded to upthread, the Soviet Union had some all-titanium hull submarines that had a better strength/weight ratio than steel and so could dive deeper. Research subs use various tricks like lightweight plastics impregnated with hollow glass beads for buoyancy, but they still have limits. The reason unmanned probes are so common now is that with fiber-optic links to the surface they can be operated remotely without the need for the hugely heavy pressure vessel that a crew would require.
As I understand it, while a sub does have to be relatively close to the surface to launch, traveling at a shallow depth allows it to be tracked by satellite. Apparently, the very small bulge it creates on the surface can be detected. If that’s true, I would think that the deeper it can dive, the better.
There’s also the issue of possibly piercing the ocean’s veil using a laser of the correct wavelength. I read about this year’s ago and haven’t heard of anything since so I suppose this was a dead end.
All military submarines has always strived to be able to go as deep as possible, both as a defensive mechanism and as a means to avoid detection. During WWII for instance, German Uboats routinely dived as deep as 200-250m to avoid enemy counterattacks (altough this was risky, as the manufacturers of the uboats generally didn’t guarantee the pressure hulls integrity past 100-120m or so.) American/British subs usually dived to about the 100m depths or so, and there never was much interest in going deepers, seeing as Japanese/German ASW tech were at the infant stage compared to the late-war Allied ASW tech.
During the cold war, subs on all sides were designed to be able to go really deep - mainly, as noted above, to avoid detection (Satelite, Magnetic detection, Acoustic detection), and would only pop up near the surface for communication, radar/EMC monitoring or weapon launch purposes. However, as others have noted, due to the technical difficulties of building a pressure hull able to withstand the massive weight of water at larger depths, and still be manouverable, there is a limit.
The US subs, generally constructed of high grade steel, had a crush depth of 500-700m and would typically operate at depths down to 300-400m. The Russian Titanium subs had a theoretical crush depth of 1300m, and would operate somewhat deeper than US subs. Still, these are probably as deep as modern sub tech allows, for military subs, at least until some new materials are discovered, and the incentive to use them is there.
The gist of it is, as other have noted, building a military sub to operate deeper than cold war era subs, make little sense, as it would be difficult and expensive to do, and depths of 400-600m really is as deep as it is nescessary to go to avoid detection from the surface - and detection underwater would be a problem no matter how deep you go, seeing as your opponents subsea equipment would probably operate at the same depths.
Another issue is that diving deep will make the hull pop from the pressure (more often the deeper you go), thus potentially revealing your boat to an enemy with good sonar.
Relating to any military utility of deeper diving submersibles, consider the deep sound channel: a depth in the ocean where sound may travel much greater distances than at other depths. From the wiki for SOFAR, it looks like the SOFAR depth around Bermuda is about 1000m. Now, you probably don’t want your vessel that deep, emitting noise that will travel much further than otherwise, but you might want a sensor package down there to hear low frequency noise that made it there from other vessels. I do not know if the sound signal from an object considerably below the SOFAR depth is materially attenuated from a sensor above the SOFAR depth. If so, then that might be another reason to get extremely deep.