Yes I read somewhere that Mac was a former military soldier but he also seemed the most down to Earth and everybody seemed to like him, at first.Because you Darrian trying to keep this thread alive I thought I should contribute by giving my view of the leadership in Carpenters "The Thing". Feel free to come up with alternative views, it will only enhance the discussion.
At the beginning of the film, the camp authorities seem to consist of the trio Garry, Dr Blair and to some extent Dr Copper. They were all civilians used to run a camp during quite normal circumstances, save for boredom and extreme winter conditions. The camp was quite informal though, and the members had quite a lot of autonomy and expertise with Macready and Clark as the most prominent examples. The group as such seems to have functioned well, even if they all had their small personal quirks.
What happened to the leadership when the sh*t started to hit the fan? My view is that it started to crumble. First off was Garry who seems to have lost his confidence after shooting the Norwegian. This I think, was a very realistic portrayal. Garry seem to only have carried his gun as a mark of authority, not really expecting to use it. Furthermore, he probably didn't have any experience shooting a man before, and he seems to got ridden of feelings of guilt/remorse. What might also be a contributing factor was that the events was so far fetched and violent he couldn't handle it, and therefore lost his will to lead. In any case he gave up/resigned from his authority quite early.
The real leader of the camp was Dr Blair but he couldn't handle the events either. He clearly understood the enormous implications of their encounter and took action long before anyone had an inkling of what was going on. Unfortunately he also understood what it meant for him and the camp and fell into a grave depression. The speed of how Dr Blair understood the series of events, even at an emotional level, suggests he was a very intelligent man. I guess that made him among the first to be targeted by the Thing (mainly because the creature realized he was a great asset/threat).
The third person was Dr Copper but he really didn't have any authority outside his medical field and couldn't be of much help, unless he got support from the other two in the trio.
So the old leadership not only crumbled but crashed. What happened after was that a fight for a new leadership ensured, with the Thing trying to affect the outcome. Macready emerged as the leader of the group after some struggle, probably because his prior experience of adversial conditions (somebody mentioned Macready was a military helicopter pilot in Vietnam as a part of the backstory) but also because he began to gain the trust of the group.
Cross lit.Childs is (enlightened - does not make sense to me). [/SPOILER]