Peter89 wrote:So why is Turkey is so important in late 1942?
This will get into my overall view of why/how the Axis should have won at least a conventional WW2, which is an ongoing project. As with your ongoing project of Germany's no-Barbarossa '40-'4? Med strategy, it's - well - ongoing in its articulation.
Turkey is the key to the to whole region between Gibraltar and Calcutta, Djibouti and Tehran (your disagreement noted of course).
From the Syria-Turkish border the Heer can (1) strike rapidly towards Suez, (2) strike somewhat less rapidly towards Basra/Abadan, and (3) can strike eastwards along the Turkish railway from Lake Van into the rear of any W.Allied force opposing the German drive from the Caucasus into Iran.
The fundamental dynamic here is that the W.Allies would face insuperable logistical difficulties defending any
of these critical axes, let alone all of them (shipping scarcity, as discussed above).
Axis possession of Suez has important consequences in the Western Med: with the RN lacking a base in the Eastern Med, Axis shipping can't be challenged there except by submarines (and these would face increasing problems as well). Torch therefore has no chance of inflicting a Tunisgrad, only of pushing the Axis east across useless deserts. But each step east exposes the rear of a W.Allied North African army to being cut off when/if Spain joins an ascendant post-SU Axis (They almost certainly would have joined, or Hitler would have swallowed Iberia as well).
The Axis drive towards Basra faces bigger logistical challenges than towards Suez but the Germans have hundreds of thousands of trucks not used by the Ostheer to support it and can build up the Berlin-Baghdad railroad. They don't need to advance much to take Mosul and its oil fields (tabling for now whether they need to or can transport its oil)
The German drive through Iran and eventually towards India has a Turkish component as stated above. In the event the W.Allies try to force a retired SU from its territory under the '41 Anglo-Soviet agreement on Iran, they're already outflanked by the German presence in Eastern Anatolia. The main German drive south from Azerbaijan has a logistics route of Black Sea - Batumi/Poti - Georgia railways as well as Russian railways (built up by Germany) - Volga - Caspian Sea - Azerbaijan/Bandar Anzali.
Here's a sketch of how the ~2 years after the fall of SU/Turkey would go:
Green arrows are late 42 and early 43, red arrows are latter 43, orange arrows are ~44. (very rough for now)
Japan's 1.1mil-man Kwantung Army, freed by SU's defeat and bolstered by German material via the humbled SU, conquers China in '43 (red arrow). Then Japan moves on India during 44 - strengthened by overland logistics from China - to meet up with the Germans there and/or waive goodbye to the British as they evacuate. I've given 2 years for the Germans to advance through Iran to India because there's a logistical wasteland in Eastern Iran and it'd be a matter of pushing forward air bases along the Persian Gulf and Arabian Sea towards Karachi.
During 43 the Axis keep moving south in Arabia from Palestine and Mesopotamia, taking Yemen by year-end. The Red Sea is now closed to W.Allied surface ships and only 20 miles separate Yemen from Djibouti. Once the Axis take that hop and push into the Horn, the Axis can steam directly between Gibraltar and Tokyo.
What would the W.Allies be doing all this time? Well they've got to commit at least some forces between Alexandria and Tehran or else the Germans can simply stroll into the whole region. Given the shipping and other logistical burdens of mounting this inevitably-losing fight, that'll occupy them through 1943 probably.
Of course they'll also be implementing their enormously-expensive bombing campaign against Germany. The fall of the SU doesn't change that strategy because the industrial momentum behind the bombing campaign was well under way when the W.Allies believed Russia would probably collapse. The bombing strategy won't work because Germany will have at least twice the plane production and plenty of fuel with which to keep its pilots on par with the W.Allies. The LW not fighting the VVS helps a little too.
The W.Allies could try to build up for a big invasion of France in 44 but OTL America maxed out at 91 divisions and it would take at least 200 to fight an undistracted Germany+allies. To build up a massive W.Allied army by mid-44 would require slashing bomber production and/or naval production in by early 43, which is implausible before the bomber strategy is tested. So the W.Allies mostly sit around in the West, maybe losing an army in North Africa, maybe losing an army in Norway, maybe pushing harder against Japan.
Japan, however, now has land and sea connections to Germany and Hitler was appropriately conscious of the need to keep Japan in the war. The three Axis powers have, between them, enough aircraft carriers to form a credible Fleet-in-Being that ties up W.Allied naval strength in the Atlantic. Because the combined Axis force can steam between Gibraltar and Aden much faster than can the W.Allies go around the Cape, the W.Allies have to abandon the Indian Ocean to Axis control. These carriers are mostly conversions of older battleships, cruisers, and liners - as was considered by Hitler but postponed OTL for good non-ATL reasons. They're not capable of defeating the USN/RN straight up but they're strong enough to force it to concentrate somewhere (Pacific and Atlantic). The orange line across the Indian Ocean is the Japanese Navy sailing to the Med, not an invasion force. With the Indian Ocean dominated by the Axis, the Axis rear is secure and their full forces can meet any invasion of their homelands.
By early '45 at the latest the Axis controls the entire Eurasian landmass and North Africa. V1's are raining down on England by the tens of thousands, the Type XXI (undelayed by crushing W.Allied bombing due to better German defenses) is biting into Transatlantic logistics, and Britain is probably ready to talk peace. With enough time for Type XXI to cut the Transatlantic supply lines, Germany can invade Britain if she's intransigent.
A-bomb aside, there's no way for the W.Allies to return to Eurasia any time soon. A-bomb included, either the parties hammer out a peace or hundreds of millions die when Japan and Germany respond to A-bombs with sarin gas and other weapons of mass destruction against their entire hemisphere.
If Turkey immolates itself rather than joining the Axis in 42 then that timeline gets pushed back a few months, which doesn't change the situation in early '45 or the strategic situation generally. It would be incongruous for a Turkish leadership class who - at best - smiled upon the Armenian genocide to prefer on moral grounds a national destruction over alliance with Hitler. The Turks would swallow the rest of Armenia, a few Greek isles, and/or a chunk of Iraq and Syria and let Hitler march on.