Not as much as you might think...the Charter of the United Nations actually
explicitly includes a provision in Article 47 for a Military Staff Committee (to be composed of the Chiefs of Staff or their representatives on the P5) which was intended to serve as essentially a Joint Chiefs for a UN military force (and still exists, albeit mainly as a place to put semi-retired flag officers). Article 45 in fact explicitly calls on members to "hold immediately available national air-force contingents for combined international enforcement action". Is this less extreme than the proposed signing over of forces directly? Yes, but at the same time it shows that the founders of the United Nations clearly envisioned a much more substantial role for the United Nations in controlling and directing global military forces than is actually the case today. It's hard to underestimate the utopian internationalist spirit which drove the early United Nations and how ready people were to at least
say that they were trying to work together with other nations in the cause of peace and goodwill and so on.
That being said, actually assigning forces directly to the United Nations for control was probably too far for all but the most internationalist of internationalists at that time. So the closest thing I could see happening to the OP's proposal is an expansion of Article 45 calling additionally for ground and naval forces to be "held immediately available," and perhaps providing an explicit formula for the share of air, naval, and ground forces that should be so held by a given Member. However, the fate of this *Article 45 would probably be the same as the actual Article 45: being totally ignored due to Cold War tensions, and thus becoming a dead letter by the modern era, with only some moribund sinecure committees and councils remaining.
At the very, very most extreme limits of possibility, I could see a UN "Rapid Response Brigade/Regiment" being formed--it clearly threatens no one by itself and, at least in theory, allows the UN to rapidly respond to crises--but it probably would only rarely be deployed at best, and would end up mostly being a propaganda and spying tool (as well as another sinecure). That would be about the most UN military power that I could see possibly being allowed to exist in any timeline where the Security Council is anything other than the playground of one nation which is mostly setting up something like the UN to be a velvet glove over their world dominance. In that case, sure, go wild.
Well, peaceful means were
preferred, yes, but the creators of the United Nations were realistic enough to realize that sometimes combat might be needed to enforce the peace. Hence Chapter VII, Article 42:
In other words, an explicit blanket authorization for the United Nations to use military force in peacekeeping operations. And, as above, Members were supposed to "hold immediately available" air forces for use in UN operations, so the creators certainly envisioned the United Nations operating and directing military forces from time to time. The idea of having a permanent UN force available is actually not much of a change from OTL, provided that it isn't clearly meant to supplant national armed forces.