"Secret base?" Is that feasible at all?
On paper, I can imagine ways and means, and paranoid Americans might figure you never can know for sure just what capabilities the USSR actually had. Certainly you can't infer from observable poverty and backwardness that they cannot possibly do X, or Y, or Z; it could be a matter of setting high regime priorities in a compartmentalized secret projects sector that for all one can prove would match or exceed the visible economy.
I'd think though to that to make sub pens with stockpiles of nuclear reloads that could serve after a full nuclear exchange would be pretty James Bond if not Tom Swift stuff. It is one thing to make hardened bunkers that can keep operating after a missile exchange. But the minimum effort necessary would leave lots of visible traces. It is another to do it camouflaged so that Power's SAC targeting team does not know they are there to strike, and then to operate while remaining invisible.
In Amerigo's scenario, the American side of the exchange quickly predominates. The missile attacks alone merely cause great decimation, but then waves of SAC bombers go rolling in. At first they take a lot of attrition and the majority of them are lost pretty soon. But eventually Soviet interception capability is exhausted and with the destruction in detail of Soviet infrastructure there is no way to recover them. Pretty soon the relatively small fraction of Western warplanes that survive have air supremacy over the USSR. And Amerigo anticipated the "secret base" possibility by postulating that patrols sweep over the wasteland territory, scouting precisely for the possibility of some base only lightly damaged rallying ragtag survivors, and drawing reserve stockpiles out for surprise late counterstrikes.
That is over land; the territory recently claimed by the USSR is vast and no surviving enemy powers have manpower to spare to occupy the place in detail.
A submarine base however must be on a coast. The Warsaw Pact as a whole suffered badly from a lack of suitable coasts! The Black Sea is a fine place with lots of Soviet coastline plus that of Romania and Bulgaria to be sure, but it is a relatively simple matter to monitor and if necessary blockade the straits leading into the Med, which localizes the threat to become mainly Turkey's problem. Someone would have to rule on just how badly Turkey was hit--surely the damn Jupiters were taken out, and I suppose as an American ally (not sure if in NATO formally yet, but that would have just been a matter of time if not already accomplished in '63) they'd get dozens or more of short-range missile and bomber strikes. So Turkey is not really in a position to defend itself, but neither is it target-rich any more. With the remnants of US and other NATO forces to simply monitor the straits, Black sea bases are useless.
The same I think applies to the Baltic.
This leaves the northwest Pacific coast and the Arctic Ocean to site these secret sub sites at. In both cases, the number of port regions where developed infrastructure gives an outlet to the large capability of the USSR to set up bases is limited, and the admittedly tremendous stretches of shoreline where in theory some secret base might be sited are difficult to access. Movements coastwise from Pacific ports to obscure locations are all too likely to be observed by prying Yankee eyes in subs and ships offshore.
The Americans have working spy sats by now, but I'd be willing to dismiss them as effective guarantees any work on secret bases would be observed. After about a dozen failed attempts the first NRO satellites only became operational very late in Eisenhower's final term and we've only had a handful of years of Kennedy admin to follow them. These satellites did not have real time transmission capability; they took photographs and send down rolls of film to be recovered, so basically the surveillance teams had to know in advance what they were looking for. However one reason Ike was so keen to develop these spy sats was that prior to them we used aircraft flying over Soviet territory to get a look-see. It was hardly possible to maintain a constant and universal watch on Soviet territory of course. But the Russians never knew just when we (or the British) would send something over. Sometimes they managed to shoot them down, sometimes they didn't. Every plane that got away with it carried valuable information and if the Russians got caught halfway through the process of setting up a secret sub base on the Arctic or Pacific coasts, we'd then know to look for more of the same.
How feasible would it be to construct something adequate for a Soviet sub to approach undetected, now that the Red Navy is no longer standing guard in their waters to try to chase off USN and RN observers and the survivors of these forces have little better to do than try to ferret out such bases?
Very few Soviet subs in 1963 would have nuclear power; the vast majority of them are diesel and need to refuel somewhere, and when making way across oceanic distances must frequently surface to snort in some air for their engines.
One thing Amerigo unfortunately gets very wrong IMHO is his notion that LBJ would recall all surviving US military forces deployed overseas to come home and help with domestic reconstruction. I agree that many of them would indeed be repatriated for such duties. But not all of them! I don't see him abandoning the near-century long legacy of "the American Century." Both parties OTL had, before WWII, substantial isolationist wings, but the men who achieved Presidential office in both were not of this camp. Woodrow Wilson was the first Democratic president since Grover Cleveland (and before him, Buchanan before the Civil War) and both he and FDR, along with Truman, wound up overseeing American power projection and global responsibility (as we deemed it anyway, others might call it something else) growing by leaps and bounds between each one assuming office and leaving it. Leaving analysis of the three Republicans who held the office between the wars aside (and while US armament growth was certainly limited in their terms, they hardly turned aside from the doctrine of "a Navy second to none" though they did try to cheapen achieving that goal with global arms restrictions) all other Presidents of the 20th century were firmly on the side of an expanding US capability and presence.
It is quite true that now, the USA has really severe problems at home that need as many hands as possible to address. And that the very large number of Americans who were in uniform when the balloon went up are now badly decimated, with their forward bases devastated when not eradicated, their forward logistics and communications in a shambles...and quite possibly, the surviving peoples in the places they more or less occupy blame the USA as much as the USSR for the misery they now eke out their survival in.
On the other hand, except for the possibility that these same miserable remnants of Europe, Japan, and elsewhere will scrape together something resembling a modern industrial base and then turn on the Yankee intruders in organized force, there is now no one left in the world who can stand against US power, despite that power being reduced to a shadowy skeleton of what it once was. A great many USN hulls have probably been sunk--but we started with a whole lot of them, and the rest have not been. Given that the Soviet Navy was fighting for its life with nuclear torpedoes, I doubt there are a lot of badly damaged and barely floating ships; most of the survivors are lightly damaged and anyway there is no foe to take advantage of the possibly weakened state of some of them. The rest are fine, although their routine maintenance and supplies are in some long-term doubt. But surely some suitable ports still exist in the USA itself--at Long Beach for instance, and probably lots of other bases on the various coasts. If the Soviets were able to make a clean sweep of all suitable ports in Europe and elsewhere in range of their IRBMs and bombers (which would imply Japan is as bad off as Europe, but I think Amerigo had them getting off less terribly suggesting some Japanese ports still survive) by that same token much lighter ships, destroyers and frigates, can dominate those waters and make do with a lot less forward support while being capable of rotating back to the USA.
Similarly US aircraft are decimated and suitable runways for the most advanced types are messed up with without resources ready to hand to refurbish them or supply them. But again the Air Force Military Air Transport Service (MATS, as it was then) can trade its surviving jet transports for operations back in the States on the majority of suitable runways still extant there, while scouring the civil market (US is under martial law and eminent domain applies) for DC-3s and so so that can operate with modern STOL type planes on very rough fields. Perhaps modern F-4s and F-101s or their European equivalents are not suited for the new Europe, but old mothballed WWII type planes can be brought out and operate with plenty of superiority over any last-ditch ragtag Soviet partisans still surviving. These are not needed in great numbers either. Civil aircraft can be retrofitted with half-assed military kit as well.
The Army was of course under fire and shot up in droves, and many of them have taken severe radiation poisoning, and possibly chem war damage too, I forget if that had much time to become a thing or not; I suspect if I go back I'll find nerve gas and mustard gas did precede the first use of nukes. But maybe not by enough that gas attacks could accomplish much before being overshadowed by nuclear strikes.
Still, American soldiers were about as well prepared as anyone could be for surviving a nuclear battlefield. This doesn't mean they survive well, but it does mean they (and NATO allies trained and equipped to a similar degree) survive better than civilians around them despite being targets. The US forces surviving and ambulatory when the nuclear exchange dies down (meaning the Warsaw Pact's entire infrastructure is gutted to the point of practical nonexistence and the last holdouts are fighting with nothing backing them up whatsoever) can and would achieve re-organization. Their prewar command and control is shot up and gone, but every unit's highest ranking officer or soldier, be that a colonel or a corporal, will accept orders from higher ranking led bodies they regroup with. Over time the US forces would thus reintegrate into a smaller but effective body subject to the orders of the President.
I don't believe then that LBJ would order all of them to board ships and planes and come home to clean up there. Leaving any behind in Europe would be a sacrifice to be sure. But it won't be a disinterested one; I think if LBJ looked ahead to the limited power and influence Amerigo grants the USA by the 21st century, he'd shudder in horror. Vice versa although the Europeans, Japanese, and others on whose soil a war was fought that the US itself largely evaded (again) might blame the Yankees, at the same time only the Yanks (and people like the Australians, maybe South Africans, Argentines and Brazilians and smaller South American nations) have the surviving infrastructure to hope to provide inputs to bring about recovery sooner in the devastated former allies. Despite officially unvoiced resentment, the quickest route to recovery and maximizing survival of the remnants of their peoples would be for the surviving fragments of NATO governments to fall in line under the banner of the continued alliance. Now the enemy is mainly the decimation of the aftermath rather than Soviet malice (though ongoing threats of rouge surviving partisans are enough to justify the military aspect of the alliance). A formal and announced "Marshall plan" might be political dynamite back home with so many millions of Americans living in worse misery than (the best off of) rescued Europeans, but simply doing it quietely--some Corps of Engineers help here, portable power generation and water purification plants shipped over to there, a whole bunch of little forms of aid simply not discussed in any detail in the US press--can make a world of difference, and bind what organization and industrial capacity can be scraped up in the shot-up terrain to US policy quite effectively. Thus, the USA retains goodwill of a sort (even with some resentment, surely individuals who are brought early on to settlements where their survival is better assured and those who need it the most have access to nearly state of the art medicines and the like must indeed be genuinely grateful, and a smart Johnson would make sure credit is shared both with their own national leadership and with Yankee benefactors.
So I don't think all the Yankees go straight home immediately, and after a few years when those left to assist in European construction while rooting out last-ditch Soviet resistance will be rotated home indeed--but only to be replaced with new American recruits trained for these duties in the recovery of the home land.
Europe would of course be mostly a bombed out ruin, with little immediate use for huge tracts of what was once prime agricultural and industrial land. But her population is also decimated. It should be possible to create a survivable and orderly life, if at far below prewar average living standards, for most of the survivors, consolidated into recovery colonies here and there. The possible mischief of separate nations seeking to readjust borders to their advantage is suppressed by the ongoing NATO alliance enforcing a simple policy of "status quo ante;" whatever West Germany or Luxembourg or Denmark had before the war is automatically still theirs, even if they agree to let some neighboring power hold some operations there a while. Their old capitals sit waiting for the fallout to die down for its own peoples to someday return, clear the rubble and start rebuilding, in the mean time it doesn't matter how awkward the locations of the refuge zones are, Uncle Sam will assist and the NATO alliance will share the burdens for mutual reconstruction.
Thus, instead of simply erasing most of the pre-War First world from the political map as they in some combination are left to die completely or turn to a slow process of isolated self-reconstruction, I believe the USA would sacrifice a small part of its own rapid self-reconstruction potential to prop up shadowy ghosts of the old allies and claim them as the surviving successors of the old order. Obviously attempting to project colonial power on any remaining overseas possessions that have any desire to leave the respective empires would be impossible. But vice versa, very few formal colonies still existed as of 1963. Congo, Angola, Mozambique and Timor as respective Belgian and Portuguese colonies would be most of what is left. If the PRC wanted to seize Hong Kong or Macau in the confusion there would be little to stop them of course.
The postwar status of the PRC is another aspect where I find Amerigo's predictions hard to square with what I'd think would be reasonable outcomes. He has a rather rosy projection in my view whereby Mao is very statesmanlike and mainly relies on soft power except for policy to the north, where he seizes control of eastern Siberia and Mongolia, and exercises hegemony over North Korea by restraining them from conquest of South Korea. In return the regional states, including ROK and Japan, move into a Chinese-led sphere where he leaves them alone internally but they harmonize foreign policy and trade with him. Neither Americans nor IIRC Soviet strikes do major harm so the PRC is free to develop as Mao sees fit.
But if the USA does not agree to withdraw from the Far East holdings we effectively had as of 1963--including Taiwan!--then I'd think Mao would take a harder line. At any rate it would not then be in his interest to do anything to protect South Korea whereas I have to agree that the USA is not in a position to fight another Korean war either. Loss of South Korea to a North that must perforce look to Chinese patronage however much they might dislike it seems very very likely and that in turn cannot fail to make Johnson look bad politically at home. A lot depends on just how badly Japan is hurt in the exchange; I suspect that American interceptors will do a very good job protecting Japan from bombers whereas the Soviets cannot afford to devote too many medium-range missiles to Japan. Still less to Taiwan or the Philippines, although Manila would be in trouble due to major US bases in the region. Again though, Soviet mid-range missiles would be hard put to strike so far and airborne bombers would not make it past the US defense gauntlet; the worst danger south of Japan would be submarine launched missiles but these too are going to be preoccupied aiming at US assets, and are subject to being decimated by USN sub-hunters before the general exchange begins.
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But Word of God for this TL is that in fact LBJ abandons all attempt to capitalize on the USA's stronger than ever relative position, in order to maximize reconstruction at home, and in effect leaves the entire world outside US borders to sink or swim by their own efforts. This is so huge a deviation from what I think he'd realistically do I can only throw my hands up and let his TL simply narrate what I regard as an improbable TL from that point of view.
So Michel, if I've forgotten that the thread has those secret bases you mention in canon, I apologize. I would ask anyone citing them as ongoing threats to explain how it is they can operate undetected. The Soviet subs seeking these ports out, and then departing them with reloads, will tend to lead watchful USAF and USN resources to infer their presence, redouble their efforts to locate them and root them out, and I'm not sure they can maintain their hidden status under such scrutiny. After all, knowing that there are some scattered and very vengeful Soviet soldiers and possibly secret installations out there, I believe Amerigo did explicitly mention extensive air patrols over former Soviet territory.