Leatherneck

Circa 1817, First Lieutenant Charles Rumsey Broom, USMC, sports a black leather stock beneath a high collar, which gave birth to the term "leatherneck"

Leatherneck is a military slang term in the U.S. for a member of the United States Marine Corps. It is generally believed to originate in the wearing of a "leather stock" that went around the neck. Its original purpose was to protect the neck from slashing blades in battle but it also served to keep the head and the neck erect when the uniform was worn.