Marines are not normally embarked in U.S. Navy warships or Coast Guard cutters. Of course, amphibious ships, some of which have small Marine detachments as part of their ship’s company, normally embark  Marines for assault operations.

It has not been announced which ships will carry Marine detachments or what will be their mission. “Maritime security” can cover a variety of activities, from inspection of merchant ships to raids on suspected pirate bases.

Since the colonial era Marines have been embarked in U.S. warships, primarily to form landing parties. In the era of steel ships Marines were assigned to cruisers, battleships, and aircraft carriers. On those ships they often were also employed to man secondary or anti-aircraft gun batteries as well as being used for landing operations. With the deployment of nuclear weapons aboard U.S. aircraft carriers in the early 1950s, Marines were given the principal duty of security for those weapons. 

During the 1990s the last Marine detachments were withdrawn from warships.  The last nuclear weapons were removed from U.S. surface ships in the early 1990s, and the last Marine detachment -- embarked in the nuclear-propelled carrier George Washington (CVN 73) -- went ashore on 3 April 1998. That detachment consisted of one officer and 25 enlisted Marines; previously Marine carrier detachments numbered two officers and 64 enlisted men.

In 1992 the Navy experimented with placing large Marine detachments aboard aircraft carriers. In January 1992 the carrier Theodore Roosevelt (CVN 71) embarked 538 Marines for a month of at-sea training and workup. This force consisted of a rifle company, command staff, and various detachments including a composite helicopter squadron.  Subsequently, in March 1993 the Roosevelt battle group steamed for the Mediterranean for a six-month deployment with some 600 Marines and their helicopters.  (Part of the carrier air wing was left ashore to make space for the Marines.)

The “TR” operation was considered successful by the Navy and Marine Corps.  However, the costs and disadvantages outweighed the benefits and the Marines-on-warship concept was not continued.

The recent decision to place Marines aboard Navy ships and Coast Guard cutters occurs as the Marine Corps is fully committed -- to the wars in Afghanistan and Iraq, and forward deployments aboard amphibious ships in several areas, while at the same time, being required to provide a major Marine troop contingent to the U.S. Special Operations Command.  The recent decision to increase the size of the Marine Corps and Army by 92,000 troops reflects the critical situation in U.S. ground troop strength. Thus, the decision to place Marines abroad ship should be addressed with caution.