The second surgical hospital in which i served was only a 60 bed hospital, very modest. The surgical hospital of the motion picture and the television hospital (i.e., from the novel) was undoubtedly a hundred bed, if not a hundred-fifty bed unit. We had six surgeons, and two internists. All surgical hospitals must be commanded by a surgeon, and surgeons who have completed their residency are promoted Major upon completing their induction training. So our hospital commander was a Major, the executive officer was a Lieutenant Colonel (Medical Service Corps) and the Chief of Nursing Services was a Lieutenant Colonel. In addition, there were, besides the nurses, a detachment commander (Captain) for the medical detachment, a Registrar (usually a Captain, as was the case in that Surg), and warrant officers who were the medivac pilots--we also had a Lieutenant who had been promoted from Warrant Officer and who commanded the air transport platoon. We were, of course, open 24-7, and a surgeon and an internist, or two surgeons, were on duty at all times.
I could go on for pages about how unrealistic the depiction of that hospital was, but i'm not the kind who lets that sort of thing spoil good entertainment for me. The motion picture, however, was a fairly accurate depiction of a surgical hospital in the field, and Altman did a good job with it.
Interestingly, by the time i was first assigned to a surgical hospital, they were no longer designated MASH. They were designated Surgical Hospital (MA), the latter acronym meaning "Mobile Army."