Let me recycle an old soc.history.what-if post of mine:
***
James Thomas Emmerson, in his book _The Rhineland Crisis: 7 March 1936_ concluded that Hitler would have resisted the French. Yes, he acknowledges, several times Hitler was to say subsequently that had the French marched in, he would have had to beat an ignominious retreat, but he usually said that to boast about his "nerves of steel", show how much more daring and wise he was than his diplomats and generals, etc. (Actually, the generals didn't put up any real opposition. Fritsch said he agreed that remilitarization of the Rhineland was a necessity, but evidently had some reservations--he agreed to it only after Hitler assured him the operation would not result in hostilities. Blomberg had no objections at all. As for the diplomats, Foreign Minister Neurath probably expressed personal reservations, but did not challenge the Fuhrer. Neither Hitler nor Neurath nor the generals thought that France would act so long as it was clear that the action was not a preparation for an attack on France--for this reason the number of troops participating in the remilitarization was limited.) The actual military orders, Emmerson claims, show that resistance was intended. Moreover, Hitler's statement to Schuschnigg in 1938, often used to bolster the theory that Hitler wouldn't resist, actually was that Germany "would withdraw perhaps 60 kilometers but would still hold the French."
An important fact to remember is that the French army in 1936 had no strike force capable of marching as far as Mainz, let alone occupying the entire Rhineland. Nor did it possess a single unit which could be made instantly combat-ready. To resist militarily, the French required mobilization, which would take time--and during that time, it would no doubt be evident how totally isolated the French would be in favoring force. Moreover, the French army believed that the Rhineland had really been militarized for a long time--they counted, besides the newly introduced troops, 30,000 members of the labor service and 30,000 members of the Landespolizei and other police organizations as combat forces. They also counted over 200,000 "auxiliaries"--all Germans in the Rhineland who belonged to such organizations as the SA, SS, and NSKK (motorized corps of the SA). These, the French believed, would put up a stiff resistance in familiar terrain, certainly for as long as would be required for Blomberg to bring in his reinforcements.
Gamelin believed that he could establish a foothold on German soil, but that his advance would be halted rapidly, both by supply problems and by the enemy--he counted not only over a million Germans already under arms but millions of members of pre- and para-military formations, disciplined, partially trained, and capable of being integrated into fighting units with reasonable speed. They might only be cannon fodder in the short run, but eventually the weight of Germany's larger population would tell, especially since France had no equivalent pool of semi-skilled manpower.
Although it is clear in retrospect that the French overestimated German military strength, that doesn't mean that an occupation of the Rhineland would have been a walkover. Hitler was not bluffing. The Aachen, Trier, and Saarbrucken battalions were under orders, not to flee, but to pull back into previously prepared positions, where their job was to "halt the enemy advance" for as long as possible before pulling back again to designated defensive areas. J.A.S. Grenville, in _A History of the World in the Twentieth Century_ (1994), comes to the same conclusion: "It is a myth that all that was required to humiliate Hitler was a French show of strength...German troops were to withdraw as far as the Ruhr and there to stay and fight. But in view of earlier French political and military decisions it was obvious that the only French counter-moves would be diplomatic." (p. 224) Hitler knew that France had not marched in March- April 1935 during the conscription crisis--and the Reich was considerably stronger eleven months later.
It is far from clear to me that if the French had marched into the Rhineland, this would have brought down the Hitler government--it might have had the opposite effect of unifying Germans around him against the invader (particularly if they saw that Britain and other nations were critical of the French move). The French, in any event, had unpleasant memories of their occupations of the Rhineland during the 1920's, and put their trust in the Maginot Line they were building.
BTW, there was one way for Germany to remilitarize the Rhineland which wouldn't even have involved the slight risk Hitler actually incurred. Hitler could simply have proclaimed that the 14,000 Landespolizei in the Rhineland were hereby incorporated into the Wehrmacht! France was most unlikely to have intervened to stop a "militarization" that did not immediately increase by even one the number of armed German forces in the Rhineland. Yet once the principle of remilitarization was established, Germany could then gradually add to their number.
I don't know why Hitler didn't choose this low-risk approach to remilitarization. Probably it was (as suggested by Emmerson) because he wanted a _dramatic_ proof to the Germans that their "slavery" had ended-- troops marching across the bridges, aircraft over the Cologne Cathedral, etc.
https://groups.google.com/d/msg/soc.history.what-if/qtvUxyKQ6hI/tVfsLI6cbMUJ