For people who find themselves at sea when it comes to choosing a career path, or for those who simply yearn to live on the open water, the U.S. Merchant Marine may be the perfect port. Here are answers to some common questions about the nation's "fourth arm of defense":

Q. What is the merchant marine?

A. The merchant marine is composed of men and women who crew U.S.-flag commercial vessels on the deep seas, inland waterways and Great Lakes. It's an industry with a wide range of opportunities, partly because there are so many different types of vessels-containerships, tankers, bulkers, passenger vessels, tugs and much more.

Q. Is the merchant marine part of the U.S. military?

A. America's mariners are civilians working for private companies, and are not members of the armed forces. However, merchant mariners crew all types of vessels, some of which are under contract to transport troops and military goods. Mariners continue to support U.S. troops in Operations Enduring Freedom and Iraqi Freedom.

Q. Where do merchant marines receive their training?

A. There are a number of maritime schools across the country. For example, the Paul Hall Center for Maritime Training and Education, based in Piney Point, Md., offers entry-level training, a program for military veterans, ongoing vocational classes, academic support and more. Since the school opened in 1967, approximately 145,000 students have trained there. The school offers academic support plus GED and college degree programs. Also, many of the maritime classes can be used for college credits.

Q. What is the training like?

A. The Paul Hall Center features top-notch educational equipment in a picturesque setting. The apprentice program blends hands-on training with classroom instruction. It consists of three phases, including 90 days aboard a U.S.-flag ship.

Q. Do graduates tend to stay in seaworthy careers?

A. Approximately 75 percent of students who complete the entire program are still sailing four years later.