Speaking as the leader of quite a few regiments, I can see some reasons why the military might not be a good fit for some autistics.
The barracks and lack of privacy
The need to obey orders (no matter how illogical) without question
The need to build some strong ties within the men and the knowledge that you can rely on your fellow soldier
The pressures of war
I'm sure some veterans can shed more light on this subject
(How I'm doing cbc? Taking the heat off you pretty good, huh?)