The Allies were scaling down their presence in 1948, not so much because they didn't think the Sovets were not a threat, but mostly because the Germans were being let off the leash more and more and an occupation force was deemed unnecessary by this point.
1948 is a pivotal period, much of the wartime military has been disbanded and military forces are in flux. Most of the US units in Germany are a mix of men who were called up in 1945-1946, but were never saw actual action, but were sent overseas to replace the war-weary veterans. Most officers are being replaced by career men and provide a good core of veterans, but many troops are raw recruits.
The Soviets probably kept as many troops as they could afford along the border, Stalin is paranoid as hell and doesn't want millions of combat trained men to be released back into the population, he's already purging the officer corps of some who took too much initiative. East Germany is down and the Soviets are still looting and kicking the body for good measure.
The Soviets are switching over to new equipment, partially to replace the old worn WWII vintage stuff and the lend-lease equipment, but it's a slow process and most troops are still using WWII equipment with rearmament happening back with picked units in the motherland.
The one thing the USSR is being mobilized for at every level is the nuclear bomb. Stalin has ordered one before 1950 and he's very nervous the West might try a preemptive strike much in the same way the Germans did so he wants that bomb at all cost. The secondary project is to increase AA and interceptor capability to defend the USSR against nuclear bombers.
The nuclear option is still misunderstood at the higher levels, while many are aware of the danger of radiation, it's not until the mid 1960's when the first scientists who worked in sub-optimal conditions are dying of cancer and other radiation illnesses. So the bombs are not considered unusually dangerous compared to our current views.
The US has worked out a plan to bomb the USSR in case of war using B29 bombers though the B50 and the B36 are being introduced. The idea is to flatten Soviet cities and industry to rob it from all available production and hub functions.
Once the shooting starts it's probable the Soviets would have an advantage. They would launch a major offensive and run over the US and British forces on the border. Meanwhile Soviet tactical air assets molest forces on the Ground and the not really great strategic bomber fleet attempts to hit major targets like Hamburg and Bonn.
They would have only a few days before the first US air units deploy in Germany, but the Soviets have a strong air force and Allied forces are now constantly targeted by tac air. AA is critically missing and underused and of little use, commanders in the field report their forces are being hammered from the air and the Soviets steamroll over their defensive lines.
Most likely the US would look for a place to regroup and link up with reinforcements, the Rhine is a likely meeting point. The British send some RAF squadrons, and mobilize troops, but it's going to take days and weeks. The US can move over some troops stationed around Europe, but it's not much in the face of the Soviet storm.
After a first few bad days, possibly weeks, US air power starts to build up and Truman would likely order a strike into Soviet territory to hit them as hard as possible, but avoiding a nuclear strike should the Soviets fail to respond.
Soviet forces are not in great shape, their logistics is starting to fail as much of the equipment they rely on is old Lend Lease stock that has been mishandled by Soviet Drivers and for lack of parts, much of it is being held together with wire and a belief in Lenin.
The first few upgraded Guards divisions arrive to reinforce the depleted front line units. They come equipped with T44 and IS II and III tanks though they are only available in small numbers and not entirely reliable.
They push towards the Rhine, where US forces set up defensive positions around major cities in the hope to slow down the advance. Some US troops are being ferried over by plane, but the majority is being shipped by boat and will take several days to reach Antwerp, Rotterdam and Hamburg so buying time is essential.
There is some good news and some bad, the US left behind a huge amount of trucks, tanks and guns, though some of it is now in the hands of European armies, there is enough to equip a few divisions. Some stock, mainly motor pools have been captured by Soviet forces who eagerly use them to replace worn equipment.
The Soviet offensive hits the line of resistance, US forces barely hold as the Soviet heavy divisions try to smash through, but the going gets tough and Germany has yet to recover from the devastation of the war, combined with demolition of major bridges and rail networks by the retreating allies.
Strikes into the Soviet motherland enrage Stalin who orders fighters to defend cities, lessening air cover for the Red Army in Germany.
Meanwhile the US and Britain are on a rampage to get allies to mobilize their forces, Belgium and the Netherlands call up forces though they have little to offer in the early days. The French promise to help reinforce the Rhine, but are wary of sending forces directly against the Soviets, still hoping a solution is reached.
The Soviets launch a final push towards the Rhine, bypassing defensive positions, preferring to isolate them, rather than to waste their effort reducing them. The Soviets are masters of operational warfare and while a bit rusty manage to coordinate major assaults by various armies, while the US and British fail to get their corps organized. US forces have taken a hammering and there are great concerns the Rhine might be crossed in a matter of weeks.
Truman sends a clear message to Stalin that crossing the line will result in the nuclear option.
Stalin pulls back his fighters to cover Soviet cities, but does not evacuate them or make preparations.
A few days later the US drop a nuclear bomb against a major Red Army concentration soon followed by a bomb on Minsk.
The death toll for the soldiers is relatively low, but the hit on morale is visible and Soviet forces pause for several days. The damage to Minsk is extensive, tens of thousands of people have died and Stalin is furious that the RKKA has failed to stop US bombers and orders fighters to take out every bomber even if it means a suicide run.
The Soviets face a major dilemma, the threat of Nuclear weapons and increased conventional bombing is beginning to take a toll on the Red Army, forcing them to abandon the highly effective concentration of force that allowed them to drive all over the Allied forces.
US troops arrive in numbers in European ports, but worldwide opinion is divided over the use of nuclear weapons.
Stalin orders his generals to make a plan to destroy the core of allied forces in Europe before the US can bring its military to bear.
He sends a message to Truman and demands that allied forces withdraw behind the Rhine and leave a 75km demilitarized zone in the western side of the river. He demands that Antwerp and Rotterdam be dismantled and forces in the Hamburg area are shipped back to the US.
Truman calls his bluff and a group of B36 bombers hit Moscow a few days later. The damage is minimal, but the blow to Stalin's prestige is so severe he orders the total annihilation of the US forces in Germany, Bagration once again, but with extreme prejudice this time.
The Soviets equip their pilots with oxygen and jury-rig system to allow their planes to fly at high altitude, but its a crapshoot and many planes crash when parts freeze.
The US are shifting as many troops as possible, recruitment offices are overflowing with veterans reenlisting. Enthusiasm is slightly less in the UK, but most people keep a stiff upper lip and carry on.
Stalin's generals have a plan to break through to the Rhine, but US bombing is starting to disrupt their supply lines and they fear that the Red Army might overstretch itself and the buildup, despite extensive Maskirovka is a tempting target for a US nuclear strike.
Operation Groza attempts to destroy the Rhine army group. Soviet Guards divisions spearhead the assault, but Truman orders the use of three nuclear weapons to be dropped on the Soviet advance. US troops are told to dig in deep and hold the line.
The attack is stalled long enough for US armoured forces to launch the first major counterattack. Soviet forces are surpised by the ferocity of the attack and the offensive fails, stopped dead by US air power and a concentrated, but costly counter-attack. Losses are high and the SOviets are now feeling the weight of strategic bombardment on their supply lines. What's left of German infrastructure is now next to useless and the Soviets discover they moved to far west.
For several weeks the battle turns into a slugging match, the Soviets have failed to break allied resolve and Stalin, refusing to see his army fall back orders the use of chemical weapons and orders a strike against the only major target within range, London.
A couple of thousand casualties and some minor damage to the city fails to break British morale.
Chemical attacks against US troops has a destabilizing effect, but Truman orders a retaliation using mustard gas and other "mild" weapons, reserving the stocks of German gas as a last resort.
Fresh divisions made up of a core of veterans, armed with modern Sherman and Pershing tanks as well as a handful of M46 Patton tanks.
Mustangs and Thunderbolts are replaced by Jets and the UK deploys the Meteor, while production of the B36 and B50 is pushing into gear.
The Red Army remains stalled in view of the Rhine, US encircled forces hold out thanks to air drops though US air losses are now higher after a few weeks than the entire campaign against Germany. The US is refurbishing everything they can find and preparing to ship it across the ocean.
Stalin's reserves are also mobilized, but they are as of yet barely a trickle and supply/transport is critically poor.
US air power is a greater threat than Germany ever was and their ground forces are getting stronger.
Truman uses third parties to communicate with the USSR in the hope to reach a settlement. Stalin's gamble and initial paranoid reaction is now putting doubt into the mind of some in the Politburo, some whisper that Stalin is now old and worn.
Another blow comes when Adenhauer declares the Federal Republic of Germany and constitutes a volunteer defense force of border guards. Although the unit is barely the size of a brigade it's another blow to Stalin's ego.
Meanwhile US air assets are reaching into northern and Southern areas of the USSR, Belarus and Ukraine, bombing cities and major industrial centers.
There are reports of uprisings in Budapest and Prague, the pro-Soviet leaders are getting nervous, but Stalin can barely spare the troops to prop them up.
The Cologne-Frankfurt-Stuttgart line is holding. US forces grab the initiative and launch an attack from the Low Countries to relieve Hamburg and threaten Berlin.
Meanwhile rumors of a mysterious disease affecting some Red Army troops related to the strange snow that blanketed the area is starting to spread. Men are dying in horrible conditions, losing their hair and teeth.
US soldiers are also sickened by fallout and casualties are sent to special hospitals so as not affect morale.
The situation in Minsk is terrible with many thousands of survivors dying in the streets, the city is closed off from the outside world. Without vital supplies the city is condemned to die.
The news of the nuclear fallout reaches Truman who decides to use tactical Nuclear weapons as a last resort though he still keeps the option to use it against strategic targets in the USSR.
Meanwhile revolts break out in Hungary and Czechoslovakia and threaten to spread to the rest of Soviet dominated Europe.
The two world powers discover they are equally matched. The USSR will not easily defeated in the field and the US does not wish to fight a multi-year war of attrition, though they have a slight advantage through their strategic bombing campaign which hardens the resolve of Stalin's enemies in the politburo who favour a return to the 1945 situation with maybe a slight advantage to save face.
The war ends by 1948-1949, Stalin might be ousted, Truman is seen as the hero who stopped the Soviets.
The Soviet ability to support North Korea or China is diminished though the Nationalists in China lack the US support to oust Mao, the Communists struggle and hold only a portion of China rather than the entire country.
The spectre of a Soviet defeat looms over future politics, their grasp on Eastern Europe is much lessened due to the brutal repression of revolts and unpopular puppet leaders.
West-Germany is a broken country and rebuilding puts her at the end of the queue in favour of France, while the UK is slightly weakened as the postponed independence of India becomes a full blown civil war.
The Soviet nuclear bomb arrives six months earlier and allows the leadership to save face. A greater and early awareness of the effect of nuclear weapons even on a small scale sees a very strong anti-nuclear movement though it does little to prevent a nuclear stand off though both sides are now very cautious about potential use.
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