The U.S. Navy has decided what to do with its "brown water navy", including three Riverine Squadrons, now that they have no overseas assignment. The coastal and river force sailors are going to be divided between bases on the U.S. east and west coasts. There they will assist with coastal and river patrol duties. The riverine force contains 2,500 active duty and 2,000 reserve sailors. There will also be opportunities for training with riverine forces of other countries, particularly in the Americas.
Organized for service in Iraq, the three riverine squadrons were rotated in and out of Iraq from 2007 to 2011. Before first arriving in Iraq the riverine sailors received lots of infantry and amphibious training, much of it provided by U.S. Marine Corps instructors. Until 2007, the army and marines had been providing most of the riverine units in Iraq. There are some sailors there as well but not as organized riverine units. In 2005, the navy established Riverine Group One, which eventually had three squadrons (each with 230 sailors and twelve 12.5 meter/39 foot boats). With headquarters and support troops the group had 900 personnel and 36 armed boats. Each boat has a crew of sixteen and is armed with machine-guns and automatic grenade launchers.
The navy riverine forces eliminated terrorist movements along, and across, the main rivers in Iraq. This was similar to the successful riverine campaign the navy waged in Vietnam four decades ago, using 16 meter (50 foot) "Swift" boats.
The riverine force was part of a larger navy effort. The navy officially established its "Naval Expeditionary Combat Command" (NECC) in 2005. This organization eventually reached a peak size of 40,000 sailors, all of whom were trained to work, and fight, on land. The U.S. Marine Corps has mixed feelings about this, for the marines have long been the navy's ground combat troops.
But in the meantime, there were plenty of sailors (over 20,000) who had served ashore in Iraq and Afghanistan. These included construction troops (Seabees), medical and other support personnel, plus advisors to the revived Iraqi navy. But the navy knew it could do more and wanted to do it with sailors, not marines.
Why not continue just using marines for this? Well, the marines do not belong to the navy, contrary to what many people think. Both the navy and marines are part of the Department of the Navy (the Department of the Army and Department of the Air Force each have only one component). The marines used to be part of the navy but over the years the marines obtained more and more autonomy. They are now, for all practical purposes, a separate service.
While the U.S. Marine Corps began, over two centuries ago, as sailors who were trained and equipped to fight as infantry, they were very much part of the navy and part of ship crews. This changed radically in the late 19th century, when all-metal steam ships replaced wooden sailing ships. The new "iron ships" really didn't need marines and there were proposals to eliminate them. The American marines got organized and fought back.
The marines performed very well as "State Department Troops" in Latin America for half a century (late 19th century to just before World War II), where American troops were needed to deal with civil disorder. During World War I they provided a brigade for ground combat in Europe, where they demonstrated exceptional combat skills. As World War II approached the U.S. Marine Corps really ran with the ball when the navy realized they would have to use amphibious assaults to take heavily fortified Japanese islands. During World War II the marines formed their first division size units and ended the war with six divisions. The Marine Corps was no longer just a minor part of the navy but on its way to being a fourth service. Over the next half century it basically achieved that goal. But in doing that the navy lost control of its ground troops.
The navy still wanted and needed land forces. So, having lost control of the USMC, the navy has created NECC. This organization contains sailors trained and equipped for land operations the navy believes it should be involved in. Some of these are still on the water, like riverine operations (small gunboats and troop carriers to control rivers and coastal waters against irregulars) and naval infantry to defend navy land bases in hostile territory. NECC sereved in Iraq, and down the road, the navy sees similar situations showing up. So, since the admirals can no longer send in the marines whenever they want to, NECC provides naval infantry, that will hop to when an admiral needs some grunts on the ground.