On several occasions, Adolf Hitler used to state that he had “a Prussian Army; a Christian Kriegsmarine and a National-Socialist Luftwaffe”. Obviously, he would have preferred to make the Army and the Kriegsmarine national-socialist as well, but it is still highly unlikely that he would have attempted such a radical reengineering of the Wehrmacht on his own initiative.
SS-Reichsfuhrer Heinrich Himmler was a different matter entirely. He had no doubt at all (and was diligently working on convincing the Führer), that the all security services (including Wehrmacht which is also a security service, obviously) had to be combined into a single State Protection Corps (a super-RSHA, if you will).
And commanded – at all levels – by fanatical national-socialists fiercely loyal to Adolf Hitler. He implied (and very probably stated it explicitly) that SPC had to be managed by him – SS-Reichsfuhrer Heinrich Himmler. And be a part of the SS, of course.
It is not clear how long would it have taken Himmler to convince Adolf Hitler to integrate Wehrmacht (or at least its Army and Abwehr) into the SS. But the generals had some very serious reasons to be worried for their very lives.
First, less than two months after the Night of the Long Knives that did away with the SA – the “second Army” of the Nazi state, Hitler publicly violated his solemn promise to the Reichswehr (that there will be never a “second Army” in the country) by creating exactly such a thing – SS-VT.
Recently renamed Waffen-SS, by November of 1941 this fearsome force consisted of seven divisions – over 100,000 men. And growing fast. The generals also were well aware of the fact that Hitler was not averse to repeat – if necessary – Operation Hummingbird.
And due to his quite open admiration of how Stalin dealt with his real and perceived political enemies (including top Red Army commanders), there was little doubt as to what his next target might be.
They were also well aware of Himmler’s firm intention to incorporate Wehrmacht (or at least the Army + Abwehr) into his beloved State Protection Corps (i.e., RSHA) via a “hostile takeover” of sorts. Bloody hostile (in a very literal sense), if needed.
Although only a small number of generals took active part in Oster/Halder conspiracy, the fact of this conspiracy was well-known to all top Army commanders. And although Gestapo (i.e. Himmler) were by law prohibited from spying on Wehrmacht, there was little doubt that such creative individuals as Himmler, Heydrich and “Gestapo” Müller would have easily found a way to get around this ban.
Consequently, the chances of Himmler finding out about the September Conspiracy and using this knowledge to physically eliminate – one way or the other – the key Wehrmacht commanders and replace them with the Waffen-SS ones (of which by that time there already were plenty), were very real.
Real enough for the Wehrmacht commanders to make a firm commitment to planning and executing a military coup – the “1941 plot”. Starting right after the Great Britain signed a peace treaty with the Third Reich.
This plot (most likely) would have been almost a carbon copy of the Oster Conspiracy (or July 20th plot, for that matter). The coup again will have been led by Franz Halder and Hans Oster and the latter will (again) assemble team(s) of special ops commandos to capture, arrest and (most likely) kill Hitler, Himmler, Göring and other key Nazi leaders.
After that has been accomplished, the conspirators will (Valkyrie-style) announce the suppression of the coup by the “rogue Nazis” and the establishment of a military dictatorship.
As Himmler’s intentions were a threat to all Wehrmacht commanders, this time there will be no “putschists” and “loyalists”. All top Wehrmacht commanders will take part in the coup and with no one to have the resources to oppose them (neither Waffen-SS nor the Luftwaffe ground units were a match for a regular Army), their success would be guaranteed.
Unless Heinrich Himmler figured out how to stop them.
The Essential Guide to Nazi Germany 