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What Is the Marine Corps Ship Sea Duty Detachment?

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Together with the U.S. Navy, the U.S. Marine Corps is part of the naval service of the nation's military. Because it's a naval service, the Marine Corps is comfortable in operating at sea as part of the Navy and Marine Corps combat team. In fact, since 1775 and until 1998, units of Marines frequently served aboard Navy ships as part of what's called a detachment. A traditional Marine detachment on a Navy ship served many purposes, including providing security and defense.

Marine Detachment History

The presence of Marines aboard Navy ships has a history going back to the U.S. Navy's forbears, the British Royal Navy. Since the birth of the Corps in 1775, seagoing Marines have routinely served aboard Navy ships. Traditionally, Marine detachments, or MarDets, on Navy ships such as battleships served as security and even attack forces as well as in various naval-specific ceremonial functions. Typically, two officers and from 35 to 55 enlisted troops made up a Navy ship's MarDet.

Marine Detachment Duties

In the decades leading up to the end of World War II, Marine detachments aboard Navy ships were used to great effect by those ships' commanding officers. MarDets once operated the confinement brigs aboard assigned Navy ships and conducted attack operations against the enemy ashore. After World War II, the duties of Navy shipboard Marine detachments evolved. Toward the end of their presence, MarDets were used to safeguard "special weapons," a euphemism for nuclear-tipped missiles.

MarDet Shipboard Life

According to Navy historians Herb Richardson and R.R. Keene, many Marine officers and enlisted personnel looked at Marine detachment duty as career-enhancing. For Marines at sea, shipboard life offered an opportunity to see the world as well as to hone amphibious-combat skills. Marines assigned to Navy shipboard MarDets had serious responsibilities as part of their ships' manpower. Marine detachments trained to fight shipboard fires as well as to go ashore and rescue American citizens.

Deployed Marine Units

The Marine Corps regularly deploys various units to amphibious troop-carrying type Navy ships. Marine Corps units deployed to Navy ships, though, aren't specifically commanded by their assigned ships' commanding officers. Rather, deployed Marine units come with their own command structure, and typically answer to a Navy and Marine Corps amphibious ready group, or ARG, commander.


Tony Guerra served more than 20 years in the U.S. Navy. He also spent seven years as an airline operations manager. Guerra is a former realtor, real-estate salesperson, associate broker and real-estate education instructor. He holds a master's degree in management and a bachelor's degree in interdisciplinary studies.

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