The "jeep cap" was first issued by the United States Army in 1942 for World War II; the purpose of the jeep cap was to be worn underneath the heavy combat helmets to offer soldiers both extra padding, and warmth. The jeep cap was originally knitted close to the head, with a six-stitch "starfish pattern" on top (supposedly to support the webbing suspension inside the helmets), with a cuff coming out like a V from the top center of the brim, and around the rest of the cap, which soldiers could pull down over their ears for even more warmth. The cap was issued in four different sizes - small, medium, large, and extra large - and made of olive drab brown (O.D. #3) wool; perfect examples of these original jeep caps can be found being worn by Staff Sergeant Kinchloe from the sitcom Hogan's Heroes (he wore his with the brim folded up), and Radar O'Reilly from M*A*S*H (who was seldom seen without one). Since then, the original jeep cap has become tremendously scarce, and hard to find; they can sometimes be found on internet stores that supply old army surplus (they usually sell for nearly $25.00), or if someone has one up for auction on eBay, this particular model has been labeled "Cap, Wool Knit M-1941".
The jeep cap has been continued to be manufactured by the U.S. Army, however, many significant changes have been made to the cap since the original issue. For one thing, the cap is now knitted very loose and deep so it can be pulled down even lower over a soldier's head and ears for more warmth (the cuff doesn't necessarily have to be pulled down to achieve this), and instead of the old six-stitch "starfish pattern" on top, it now features a simple, more modern four-stitch topping. The cuff is now knitted completely around the entire cap, rather than coming out like a V at the center of the brim; also gone are the days of the cap being issued in four different sizes, as modern yarns are elastic enough that they are "one-size-fits-all". Another significant change that has been made is that the cap is no longer made in the color brown, but rather standard olive drab green (to match the rest of the Army's uniforms), and is also available in navy blue, and black. Probably the only thing that is the same about these and the original jeep caps are the short brims, and that they are made from knitted wool. Today's model are labeled "Cap, Knit Watch RN-93084".
Due the rising popularity of the jeep cap (mostly by rappers, skateboarders, and outdoorsmen), various sports companies, such as Nike, manufacture their own version of the jeep caps: these are generally made to resemble the one issued by the government, but are made cheaply out of acrylic, rather than wool, and are also manufactured in an endless variety of commercial colors, and some cases, also have embroidery designs on them; Wal-Mart even stocks jeep caps that have brown brims and cuffs, and a Camouflage cap made from fleece. These are also manufactured in "one-size-fits-all", but in most cases, because of their tighter knit, they are labeled "one size fits most". These caps are usually found in department stores as seasonal items (for autumn and winter), or sporting goods stores and stores that sell outdoor clothing.