I know this subject has been touched on a few times in other posts. The ones I found so far:

Gorman's OD Uniform

and

Drake's Hat

...plus mentions in other posts.

But what I did not find listed is information on the EXACT cap worn in the film by Lieutenant Gorman, Drake, Frost, and shown as part of the early Spunkmeyer uniform. Most everyone just posts that it is a "Vietnam-era Hot Weather Cap", which is NOT entirely correct.

The CAP, HOT WEATHER [the official United States Government nomenclature for this item] was manufactured from 1962 until 1987. There are THREE distinct versions [or variations] of this cap.

TYPE I

CAP, HOT WEATHER [NSN 8405-00-823-7178-series] - manufactured from 1962 until approximately 1972-73. Made from gabardine. Constructed of six pieces [plus the bill]. Each of the six pieces has a vent hole. This cap DOES NOT have the front stiffner. Color is U.S. Army Olive Green Shade 106 [OG-106]. This is NOT the cap worn in the film as all the caps worn have the front stiffner and DO NOT have vent holes in the front two panels.

TYPE II

CAP, HOT WEATHER [NSN 8415-00-177-4834-series] - manufactured from 1973 to 1975. An improved version of the TYPE I cap. Still manufactured from gabardine in OG-106. The front two vents holes are eliminated and the front stiffner is added. This is to give the cap a more "military" appearance - instead of looking like a "flop hat". It is very doubtful this cap was used in the film as it was not manufactured for very long before the TYPE III was introduced.

TYPE III

CAP, HOT WEATHER [NSN 8415-01-072-8716-series] - manufactured from 1976 until 1987. Identical to the TYPE II cap but constructed from cotton and polyester. Color is changed to U.S. Army Olive Green Shade 507 [OG-507]. This cap utilizes stronger and more durable materials that allows the cap to retain it's shape better than gabardine. Plus it does not fade like gabardine.

The caps utilized in the film are most probably [95%] this type of cap due to:

[a] the slightly darker color of OG-507 - OG-106 gabardine is a shade or two lighter
[b] the caps worn in the film are very "sharp" - OG-507 caps hold their shape much better than the gabardine ones
[c] plus the fact the TYPE II cap was only manufactured for a few years makes them less common and harder to come by [NOT impossible - there were a lot manufactured]

The TYPE III cap is definately more COMMON [in 1985-1986] than the other two types and were also more readily available.

NOTE: the TYPE I, II, III designations are not "collector" or military designations - it is just something I added to sort out the different variations of the cap.

Hope this helps.