Suspiciously, Wikipedia is very hush hush about sweater protocol in the United States Military. I couldn't find page on military sweater etiquette. If I were an enlisted man, I wouldn't know the appropriate times to wear snappy little numbers like this Khaki Commando Sweater (priced from only 39.95 at Army Navy Stores).
Granted there would be more pressing issues. I think the khaki commando would be dashing over a cup of instant coffee, drunk with a group of fellow officers at camp. Tragically, The days when it was hip to wear a sweater on the front line have ended. This soldier looks a bit too...editorial to be taken seriously in accordance with our post-WWII standards of masculinity.