1) I think it is well enough established--Stalin has no motive to want a war in the mid-40s. All the liabilities that suggest the West might win would be painfully well known to him.
2) If western air forces are so damn superior*
and the Americans have The Bomb, how feasible then is a Western victory over the USSR, if hostilities start in 1945?
The catch about the atomic bomb is, the Americans have--a classified number of them; even President Truman did not know how many--he, in General Leslie Groves's opinion, did not need to know that. But in 1945, they'd be counted in single digits. After Nagasaki I am not sure we had even one more Fat Man bomb actually ready to go; it would not have been prudent to use the last one in case the Japanese were to remain so defiant as to challenge us to an immediate encore, to prove it wasn't a one-shot trick, I suppose, but we couldn't have had more than a couple more ready if that.
The catch here is the same thing that is the major factor inhibiting proliferation of nuclear weapons to this day--it is not easy to come by weapons-grade fissionables. The USA alone had at least two parallel tracks turning out such materials, U-235 and plutonium--but it was trickling out of them. I'm not sure if Britain had any processing going on after they turned over Tube Alloys information (and people) over to the USA--I suspect they suspended such operations and hoped the Americans would succeed (and share as the gentleman's agreement between Churchill and FDR promised--which we did not.
)
So--weapons-grade materials for Fat Man bombs were in very short supply; the slow rate at which they accumulated accounted for the delay until that design could be tested at Trinity and then the delay of more months to be ready to use it on Nagasaki--it took that long to accumulate enough plutonium to then assemble the next bomb.
Obviously the folks at Oak Ridge and Hanford and new plants were able to pick the pace up over the next decade; by 1950 I suppose we had hundreds of bombs of various sizes and types on hand, and had expended quite a few more in tests. But as late as the
Operation Crossroads tests at Bikini in July 1946, there were, according to
Jonathan Weisgall's 1994 book on the subject (which IIRC I've read) there were a grand total of
seven bombs in the US inventory!
(If there were zero after Nagasaki, then that implies it would take almost two months to accumulate the plutonium, which jibes pretty well with the interval between the Trinity test and the attack on Nagasaki--if we had a prudent reserve of one or two on hand then, it implies an even slower pace). Crossroads was the first test after Trinity and the wartime use on two Japanese cities, so there weren't more bombs that had been used in tests by that point. The Wiki article repeats some of what Weisgall discussed in the book about the political controversy around the tests, which came from different directions--it is very noteworthy, in discussing whether the Western powers would have the will to attack the USSR, that opposition included veteran's organizations, on the grounds that it was obvious sabre-rattling intended to intimidate the Soviets.
Another opponent, IIRC, was General Groves--who obviously would be concerned about depleting nearly half of the USA's total nuclear arsenal on three test shots. (Only two were actually detonated--the "Charlie" third shot, a planned detonation in deep water, was abandoned after the "Baker" shot in the shallow water of the lagoon wrecked much unexpected havoc in the form of radioactive fallout, which badly disrupted Navy plans to salvage ships and investigate them--to save many of the ships from the initial blast damage would have been possible per USN damage control procedures, but not when they were drenched in lethal levels of radioactive water and mud!)
Another lesson the book highlights was the imprecision of Groves's favored B-29 bomber crews--despite their training and operating in peaceful, relatively safe and unhindered test conditions, they missed dropping the first, Able, airburst shot on target by more than 600 meters (which invalidated a lot of the prepared test conditions on the various ships jam-packed in the harbor). 600 meters off is not going to make much difference in trying to destroy Leningrad or Moscow, true--but how much more would desperate Soviet anti-aircraft measures spoil the aim of these crack crews in serious wartime? It also casts doubt on the possible use of nuclear bombs tactically, to take out large concentrations of Red Army force--either the Americans, overconfident of their allegedly precision bombing, would waste some of their precious handful of bombs on trying to eliminate such a concentration but then miss by half a mile and more, thus failing to eliminate the full force they intended (the Soviet soldiers who were missed might be dead men walking from fallout exposure (if so, so would Western allied soldiers engaging them likely to become as well
) but could probably fight on for some days anyway). Or learning or anticipating these battlefield lessons they'd reserve the big bombs solely for the role of eliminating Soviet cities (hardly the best method for telegraphing one's good will and intention to come as liberators, though a fine enough one for establishing a reputation of ruthless viciousness and spreading sheer terror I guess).
Can they get the bombs to the cities? The B-29 has the range, and good speed at high altitude to make it a difficult target to take out to be sure, especially if each bomb-carrying plane is accompanied by an armada of other B-29s tricked out to look like the nuclear-carrier modified version, leaving the enemy guessing which one of dozens to concentrate on shooting down. And it is certainly true enough OTL that for many years to come after WWII ended, various western planes on scouting missions--including the giant but piston-engined B-36, IIRC, and certainly later Canberra and jet B-47 missions--accomplished amazing feats of penetration, eluding all Soviet air defenses on "spy" flights.
If the USA had hundreds of bombs and hundreds of bombers to carry them, we can be pretty sure the majority of them would find their targets and destroy them (at least soft targets such as cities; it might take real precision work to take out bunkers) despite the improved Soviet state of air defenses well after 1945. I don't know that most would get out again, but their mission would be accomplished.
But in 1945 the USA does not have hundreds, nor even dozens, not even ten--the sooner we imagine the gung-ho Western assault happening, the more pathetically small the handful is. If the USA has just one bomb, are we going to risk it running the gauntlet of all the air defense the Soviets can muster or improvise, to reach a distant target like Moscow? I suppose if the war can be supposed to happen, Leningrad would not last long, and if the Russians in the Far East are enough of a nuisance, Vladivostok might not last much longer. But the deeper into Russia the strike must run, the more epic the task and risk of delivering that one available bomb all the way to its target, the greater the odds that the mission will fail and even result in delivering a good chunk of weapons-grade fissionables straight into the hands of Stalin's top cop Lavrenti Beria, to hand over to Dr Kurchatov or the young hotshot Sakharov to fashion into a bomb of their own.
Possession of the infrastructure to make atomic bombs will be an advantage, but it won't be a war-deciding one for years.
Consider the geography--Western forces will be face to face with the bulk of the Red Army, based in their conquered Eastern European territories as much because behind them, the Soviet Union is a devastated wasteland that at the moment has little housing or food for them as because Stalin wants them there to occupy the territories. The Army in Europe is in range of the western air forces (inasmuch as we discount the ability of the Soviet air forces to keep them out, which we do at our peril) but not concentrated in any one place enough to make a nuclear strike cost-effective. Behind them--a vast wasteland under painful reconstruction--Groves's bomber can probably reach Minsk all right but is it worth a nuke in its current state of disarray? And far to the east--the lands the Soviets managed to keep Hitler out of, including Moscow itself to be sure--but even nuking Moscow will not have the same effect as say taking out Paris would have on France. During Barbarossa the Soviet regime evacuated Moscow (except for Stalin himself, who defiantly stayed there--he won't do that if he thinks the city might be nuked though) and moved farther yet to the east, to the Urals and beyond, where factory cities built in the 1930s operated all through the war beyond Hitler's reach. If the US air forces can strike that far, they can start to mess up the real industrial core of the Soviet Union that fought the Great Patriotic war. But no one target will mean "game over." If over several years the ruined centers start adding up to numbers counted in tens, I suppose that will amount to a serious sapping of Soviet abilities. But the Western armies must in the mean time endure fighting the same army that stopped Hitler's legions and dogged their heels back home until they had no more homes left to retreat to.
So never mind that the Americans have nukes. If they are truly resolved to crush the USSR they can I suppose keep the Russians so occupied they have no time and resources left to make any nukes of their own--for one thing, while eventually sources of uranium were found deep in the USSR itself (you can find just about any mineral you like in Siberia, if one can endure the conditions or anyway force some slave-prisoners to, and has the time to look--they even found helium eventually) in the mid-40s I've been told they didn't know of them and had to get all of it from eastern Europe--from East Germany at first, later of course from Czechoslovakia. I suppose the Western assault will deny them those sources.
But while the West need not worry the Soviets will eventually retaliate in kind, the handful they have available in the mid-decade are effectively irrelevant to this anti-Soviet crusade. Wait a decade and of course it is an entirely different matter. For now, it is a long hard grind of conventional force against conventional force.
Given the will, I suppose the USA can back up sufficient effort to grind the Red Army down. If one is counting on Soviet capitulation one is being foolish though. Nothing could validate Kremlin propaganda that equates the capitalist-ruled West with Hitler's manic regime than such a brutal and unprovoked second attack on the Motherland, and this time they are dug in far west of their old frontiers. Most of the fighting would happen there; if the West can win, it will happen west of the old Soviet boundaries, finishing the job Hitler started on turning Eastern Europe into a charnel-house wasteland. The Soviets will obey orders to fight for every meter of ground and to the death, knowing it is the only protection of what is left of their homes. They'll strip the land of every resource it's got, to provide cover for what pathetic logistics their vast rear can supply them with. Perhaps the Western forces can prevail, but (assuming calls for truces fall on deaf ears) only by killing off pretty much the whole Red Army. The day will come when there just aren't any defenders left, then they'll break through, to find pathetic but desperate waves of women an children still fighting them.
So if a war of extermination is the dream one wants to pursue, yeah, I suppose maybe the USA might have the sheer industrial potential to accomplish the task, and celebrate mass murder on a level Hitler could only dream of with a dozen nuclear strikes on a dozen Soviet ghost towns afterward, I guess.
The Russians will exact a toll in blood of course, not to mention the sheer economic cost of the military logistics necessary to equip the Western crusaders with the munitions they need to kill the Soviet people in order to save them. I believe the statistics of the German armies fighting their various enemies bear out that they took several of their enemies with them for every one they lost, and I think their kill ratio was even better than average on the Eastern Front. Just suppose the well-equipped Western armies all to a man manage as well as the Germans did on their eastern marvelous adventure, and so, take the number of Red Army forces in uniform in 1945, and divide by say 4. These are the casualties the Western forces can minimally expect.
I have none of these numbers handy. I'm going to guess they are all terribly high though.
Now--with people like Harry Truman, Winston Churchill, Clement Atlee, General Eisenhower, and all the hundreds of other top generals and admirals and political top leaders of the Western nations all well able to estimate these likely costs, just what exactly could motivate them to decide to order such an assault, just months after witnessing what it did to the Third Reich? After several years of telling the democratic publics of the USA and Commonwealth that the Soviets were our staunch allies and we'd build a better world alongside them once Hitler was gone?
I honestly am not sure the feat of turning that wartime message around and getting the American and British people behind years more of the same old grind to bump off one of our allies would be impossible; certainly the Soviets had plenty of ill-wishers before Hitler gave it a bad name. There is certainly the issue of Poland to stand firm on--Britain went to war in the name of Poland's freedom, it might work to assert the Western allies cannot rest until Poland is free again. (Never mind Poland will be effectively ground out of existence by this particular endgame; the principle is surely the thing!
)
But as long as the Western allies retain some vestige of democracy (which they did very strongly in the OTL war) quite a few people will question this sudden turn, and demand some sort of explanation. Support will not be as widely and deeply forthcoming as for putting an end to the Third Reich and Japanese aggression, whereas the sacrifices needed will be just as stark.
So, what would the Western leaders be telling the public? Exactly what motivates this?
Why do they fight, on such a scale?
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*Remember, the Soviets not only beat the Wehrmacht--accounting for some 2/3 of all European Axis losses in men, and 3/4 their losses in tanks--but beat the Luftwaffe too--not by as impressive a margin, to be sure; they "only" cost Hitler and his allies just half their aircraft losses. But they certainly know a thing or two about defending their air spaces!