Coast Guard 47' Motor Lifeboat in Morro Bay, CA 04 Dec 2007

A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland (lakes) or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a vessel small enough to be carried aboard another vessel (a ship). Another less restrictive definition is a vessel that can be lifted out of the water. Strictly speaking and uniquely a submarine is a boat as defined by the Royal Navy^{[citation needed]}. Some boats too large for the naval definition include the Great Lakes freighter, riverboat, narrowboat and ferryboat. The term armed boat, used primarily by English speaking naval forces, referred to any boat carrying either a cannon or armed occupants, such as marines^{[citation needed]}.

A coast guard or coastguard is a maritime security organization of a particular country. The term implies widely different responsibilities in different countries, from being a heavily armed military force with customs and security duties to being a volunteer organization tasked with search and rescue functions and lacking any law enforcement powers. However, a typical coast guard's functions distinct from typical functions of both the navy (a pure military force) and a transportation police (a mere law enforcement agency).

The United States Coast Guard (USCG) is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the U.S. military branches for having a maritime law enforcement mission (with jurisdiction in both domestic and international waters) and a federal regulatory agency mission as part of its mission set. It operates under the Department of Homeland Security during peacetime, and can be transferred to the Department of the Navy by the President at any time, or by Congress during time of war.

Founded by Alexander Hamilton as the Revenue Cutter Service on 4 August 1790, it is the United States' oldest continuous seagoing service. As of August 2009^[update] the Coast Guard had approximately 42,000 men and women on active duty, 7,500 reservists, 30,000 auxiliarists, and 7,700 full-time civilian employees.

The Coast Guard's legal authority differs from the other four armed services: it operates simultaneously under Title 10 of the United States Code and its other organic authorities, e.g., Titles 6, 14, 19, 33, 46, etc. Because of its legal authority, the Coast Guard can conduct military operations under the Department of Defense or directly for the President in accordance with Title 14 USC 1–3.