The Garrison Cap originated during World War I. The French soldiers wore a cloth cap that was the inspiration for the U.S. Army "overseas cap" adopted during World War I, but that cap was not used inside the U.S. By the late 1930s the cap was altered for use by both officers and enlisted men, and piping was added to indicate the branch of service. Since it was used in the U.S. as well as overseas, it became known as the Garrison Cap.
During World War II the Garrison Cap was widely used by all services in wool OD and in khaki.
Cap, Garrison, OD -- wool serge, no piping.
Garrison Caps were produced in dark OD wool as well as in khaki to go with the khaki cotton summer uniform. There was also the "Cap, Garrison, Wool, Elastique, OD, Dark, Officers". Officers garrison caps were worn with officer's insignia pinned near the front on the left side (except until mid-1942, before which unit insignia could be worn). The USMC had its own garrison cap, similar in style to the Army version but in USMC forset green color
Garrison Cap Piping Colors
The piping on the Garrison Cap was referred to as the "hat cord" or "braid" which were either pure colors or a base color with a second color "piped" into the cord. According to FM 21-100 Soldier's Handbook, dated 11 December 1940, the hat cord colors for the arms and services were:
Cap, Garrison, OD -- wool serge, US Army Air Corps piping.
Ultramarine blue piped with golden orange
Chemical Warfare Service
Cobalt blue piped with golden orange
Coast Artillery Corps
Corps of Engineers
Scarlet piped with white
Silver Grey piped with golden yellow
Infantry and Tanks
Maroon piped with white
Yellow piped with green
Crimson piped with yellow
Orange piped with white
In 1940, with the issuance of the Dark Elastique garrison cap, gold braid was authorized for general officers, gold/black for other officers, and silver/black for warrant officers. Other piping was changed during the war as the Army changed organization. The Armored Force separated from Infantry and adoped green with yellow piping as its colors, and Transportation Corps was established with Crimson and Gold (hard to distinguish from Ordnance).
Find More Information on the Internet
There are many fine websites that have additional information on this
topic, too many to list here and too many to keep up with as they come and go.
Use this Google web search form to get an up to date report of what's out there.
For good results, try entering this: garrison cap. Then click the Search button.