Each boat has a crew of sixteen and is armed with machine-guns and automatic grenade launchers. The navy is attempting to eliminate terrorist movements along, and across, the main rivers in Iraq. This is similar to the successful riverine campaign the navy waged in Vietnam four decades ago, using 50 foot "Swift" boats.
The navy officially established its "Naval Expeditionary Combat Command" (NECC) a year ago. This organization will eventually grow to contain 40,000 sailors, all of whom will be 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 are plenty of sailors (about 10,000) who have served ashore in Iraq and Afghanistan. These include construction troops (Seabees), medical and other support personnel, plus advisors to the revived Iraqi navy. But the navy knows it can do more, and wants to do it with sailors, not marines.
Why not continue just using marines for this? Well, the marines do not belong to the navy, as they are often described. 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 from the navy. 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 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 will contain 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. There's a need right now 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.
The U.S. Navy's new amphibious unit, Riverine Squadron 1, was supposed to have had troops in Iraq this year. But there were the usual delays, the main one being the perceived need to provide some intense training for the sailors who would be manning the boats, and doing the fighting. So the first riverine units are undergoing more infantry and amphibious training, much of it provided by U.S. Marine Corps instructors. Until now, the army and marines have been providing most of the riverine units in Iraq. There are some sailors there as well, but not as organized riverine units. The navy unit currently being trained, Riverine Group One, will have three squadrons (each with 220 sailors and twelve 39 foot boats). With headquarters and support troops, the group has 900 personnel and 36 armed boats.