I have to point it out again that SIOP-64 mentioned, although without specific weapon names, 'survivable force' would be used for 2nd strike and 'accurate and rapid reaction force' would be used in 1st strike. Or SIOP-62, please teach me if I'm wrong.
Anyway, silos are way off 'survivable force' and SLBM is way off 'accurate and rapid'(compared with silos.)
All that is about guess but we can always choose better assumptions. Firstly let's fix on 1970s. I mentioned SIOP-64 and NSDM, of course you can always hold your own assumption but there's no evidence for me, anyway it's all about guess so just believe what you believe.
Now we are in 2020, and US silos only contain ~400 warheads while most warheads are deployed in SLBMs. How is it possible that "land based ICBMs contribute much of the sheer volume of munitions needed to generate an effective counterforce/countervalue salvo"(your own words)?
Last but not least, how those stories can be linked with B-21 and LRSO?
Yes, I am aware that within SIOP-64 there is mention of the need to employ "survivable" forces in second strike operations and to possess "rapid reaction" nuclear delivery mechanisms to conduct prompt counterforce/damage-mitigation. This, however, is much less of a feature of the overall disposition and weaponeering methodology and is FAR more to do with political considerations and US strategic deterrence outlook.
Indeed, the US's second strike capability currently is all but singlehandedly placed upon SSBNs, however that isn't what we were discussing. To jump ahead for a second to your point about the B-21 and LRSO, you initially conceived of a scenario in which the US launches a non-"preemptive" (I make distinction because, since you've read SIOP64, you're probably aware that the scenario considered closest to a true first strike while still remaining plausible was a prompt, pre-emptive counterforce attack on an imminently operating Soviet nuclear delivery system; which is meaningfully different from a "true" first-strike in objective and conduct) first strike attack conducted in a manner that had B-21s making first contact with the PLA counter-air complex before any other platforms had been employed. This, simply, is not a reasonable condition to encounter, and I'll get on to why in a moment.
Back to SIOP-64. One of the most fundamental goals of SIOPs post SIOP62 was to establish multiple response options with flexible target sets, force employment schema, delivery platforms, reserve-thresholds, etc. etc. This is mostly due to the original SAC nuclear attack profiles being horrifically wasteful, and being entirely divorced from other services (often resulting in redundant targeting); while being extremely inflexible in their overkill (per the "Massive Retaliation" doctrine lol). Some of these schemes indeed involved around SLBMs providing the brunt of the yield, but these were
always as part of piecemeal profiles and not full "strategic, bandwidth to magazine depth" nuclear attack profiles. In the event of a MAO-1 style bandwidth to magazine depth profile, joint planning is more oriented towards employing SLBMs in that "door-kicker" role throughout most of the cold war.
Where you *are* outright wrong is in the statement that no platforms were specified in these SIOPs. There's a fantastic read that I highly recommend, entitled International Security (vol.7 no.4) from 1983 that discusses the overall nature of US nuclear planning and force employment, as well as delving into more depth about the attack profiles during these periods. On page 4, you will find,
"
of approximately 1050 Designated Ground Zeros (DGZs) for nuclear weapons, including 151 urban-industrial targets. Given sufficient warning, the United States would launch its entire strategic force carrying 3500 nuclear weapons against the Soviet Union, Communist China, and the satellite nations. At the very least, an "alert force" composed of 880 bombers and missiles would attack some 650 DGZs (including 170 defense suppression targets) with over 1400 weapons basing a total yield of 2100 megatons."
This, though tacitly, shows the significantly larger utilization of strategic aviation in "volume" target prosecution. For the overwhelming majority of DGZs, strategic aviation was the platform selected to generate effects (due in no small part to the relative "cheap"ness of gravity bombs compared to SL/ICBMs, and the much larger quantities of which are able to be stored). Throughout the cold war as a whole, the ratios of delivery system were far far different than we see today. At its height, SAC wielded more than 700 B-52s and close to 2,000 B-47s, which could deliver 20 and 4 nuclear weapons per airframe respectively. These numbers were necessary to conduct the multi-thousand-munition attack plans that were envisioned, and were by far the optimal platforms for employing the gargantuan nuclear inventory possessed by the US at the time.
That is what I mean by SLCMs being responsible, in a full-bandwidth first strike employment scheme, for initial prompt, minimal-warning fires against crucial targets, which then enable cheaper, less penetration-capable platforms (alongside ICBMs and other land based systems, which would also contribute to the initial counter-nuclear and defense suppression/destruction) to leverage their far greater numbers, ability to return to their basing (nominally) and continue to generate strike sorties, employing many thousands of additional warheads, long after SLBM and ICBM silos are empty of their munitions.
While yes, I absolutely do agree that SSBNs contribute a far larger percentage of the total yield to any given nuclear attack profile these days than they did in the past (if simply due to the massively reduced strategic aviation airframe numbers, and the non-MIRV silo'd ICBMs), it is still worth noting that despite being the highest warhead-count in *active* service, there still are a very large number of air-deliverable warheads in storage, as well as a sizable number of silo-launched ICBMs. This, though, can also be attributed largely to the overall reduction in global nuclear threat scale, as well as a shift in thinking away from a nuclear-oriented mentality stereotypically attributed to Cold Warriors.
Thus, this brings us back to your final question. What does this have to do with B-21 and LRSO. Well, in a nutshell, my point is that due to the employment doctrine, force structure, and requisite mindset inherent to an overt nuclear first strike, it is
extremely dubious to suggest that B-21s will form the initial point of contact with the US's nuclear delivery systems, and that slow, large, and highly valuable (albeit far more survivable than its bomber predecessors) airframes such as B-21 will be conducting abject nuclear bombardment without the myriad of other assets (such as those aforementioned SSBNs) ensuring that the PLA's counter-air complex is in shambles by the time the Raider enters the threat environment. At which point, the B-21 is sort of the least of one's worries. It is simply a nonsensical scenario that has no basis in doctrine, sensible employment, nor force design, and I find it ridiculous to even assert that it is plausible.