Before the BDU's came out, that POS was the only authorized fatigue uniform headgear in Korea from October to April. You had to fold it up to look like a half fast state troopers hat and pin your rank on the front. Looked dumb. A lot of people bought BDU's who weren't yet required to have them just to get out of wearing that stupid hat.
They still use that thing as a helmet liner.
My artillery unit had them and insisted we use them.
*ptui!*
We used what we could to avoid that thing like the plague.