I have only vague data on MX deep sea deployment.
SAC affect Buried-Trench Mobility were the MX move random on Rails and brake true tunnel roof in case of War, the BTM needed 3000-6000 miles of Tunnels !
and there wee also this idea
the Lake-Bottom Mobility, MX in canister are move on back of a "lake bottom crawling vehicles" or "submerging missile barges"
see this link for mire info
http://www.secretprojects.co.uk/forum/index.php/topic,1063.0.html
According to the (very limited) documentation I've found, ORCA was going to be canisterized MX missiles tethered to the ocean floor on the continental shelf. No manpower on site, just a canister and a tether. Never implemented because it violated the Seabed Treaty and was vulnerable to attack without corresponding advantages. I've never found anything about deep sea basing, but it wouldn't surprise me - they considered everything else, after all.
i found this picture of 1966 US Navy study for underwater Base called "Rock-Site"
Ooooh, pretty! Thank you very much, I've never heard of this.
It does give me ideas, though, if we want to drive the military to invest in deep undersea bases rather than just submarines. I'm going to turn off the plausibility filter for a minute here and start brainstorming.
I've been toying with the idea of a more widespread, earlier adoption of protracted war concepts in nuclear strategy. A deep undersea base
might be useful if you're anticipating a nuclear conflict long enough that resupplying and repairing submarines, to a degree that you can't achieve with surface resupply vessels, would be desirable. The base would be deep enough underwater that ballistic missile attack is impractical, and could be defended against torpedo attack by submarines. Alternatively, it might be buried deeply enough underground that it could survive a direct nuclear hit, and rely on multiple redundant ingress/egress channels and/or stored tunneling machines to maintain links to the outside. The base would allow you to sustain submarine operations, both SSNs and SSBNs, for at least a year even in a strategic nuclear conflict.
Alright, plausibility filter back on. I don't actually think the above makes sense; it's too expensive and impractical compared to surface resupply ships, even if it offers theoretical advantages. But maybe someone can come up with something actually plausible from it.