Military Side Cap

One of my chosen hats is the flat pattern military side cap, from WWII. As my theme is the war years, it seems necessary to include a hat which was seen on the front Linea, and not just on home turf. There are several styles of the cap, depending on location, rank and duties. The main structure of the cap is one 'lid' section inset between the two side panels. This is consistent between all the hats. Some are high in relation to the hat and many have front buttons.
I am also looking into other films where the hat is used, and I have found Sky Captain and The World of Tomorrow. This uses a semi futuristic/war era setting, fusing time and costume from the past and the future.