Serving in any one of the branches of the United States military has always lent itself to a colorful vocabulary. To employ a parachute is to “hit the silk.” A destination could be 20 kilometers, or “klicks,” away. A flashlight might be referred to as a “moonbeam.”

Many of these have pretty obvious connotations, but one term is a little more ambiguous. Some service members refer to members of the Marine Corps as “jarheads.” Why? And what is it in reference to?

There are a few theories. The Marines, which were founded on November 10, 1775, as a subset of different military branches and later became its own branch, have long made use of a high-collar uniform. The collar, originally made of leather, once led to a nickname of leathernecks. That high collar is thought to have given a Marine the appearance of their head sticking out of a jar, leading to the “jarhead” moniker being adopted around World War II.

There’s another physical trait that may have led to the name. A trademark Marine haircut is short on the sides and a square, flat look on top, which may have appeared to some like the lid of a jar.

It’s also possible that the jarhead label referred to more of an overall Marine attitude than any physical characteristics. Marines have long been considered durable and able to endure challenging physical training, leading to a belief among other service members that they’re hard on the outside and able to hold whatever beliefs or orders have been handed down on the inside.

This theory might hold more water than others, as “jarhead” was once a slang term for a mule used as early as 1918. Considered a loyal and hardworking animal able to follow orders, it’s possible the jarhead name was ported over to Marines, who saw it as a favorable comparison.

While the jarhead label may be well-received or not depending on the Marine in question, it’s believed that many Marines embrace it, since it designates them as unwavering in their sense of duty.

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