The USCG is the smallest of the United States' five military branches, but also unique in that it has some law enforcement jurisdiction and is operated by the DOH during peacetime. They perform search & rescue operations, protect ports and harbors, and stop drug smugglers, among other things. Although described by some as Navy washouts, the USCG performs very dangerous duties even during times of peace.

A sea-based branch of the United States military that is jointly operated by the Department of Defense and the Department of Homeland Security. During times of war, they assist the Navy. During times of peace, their general duties include: border patrol, immigration control, environmental protection, search and rescue, and stopping drug trafficking into the Untied States.

Those who police the police.

The smallest of the five branches of the U.S. military. They are under-funded and under-appreciated, but they are vital to national security. They conduct search & rescue, counterterrorism, customs & immigration enforcement, and environmental law compliance tasks.

That hard nucleus of seagoing professionals around which the Navy forms in times of war.

The hardest working and most important of the United States' 5 armed services, performing search & rescue, drug and illegal immigrant interdiction, as well as port security.

The oldest sea-going branch of the military and most unknown. Under the Department of Homeland Security, the Coast Guard's main mission is the safety of personnel and property at sea. 98% of Coast Guard assests are comprised of hand-me-downs from the Navy.

A rather unique branch of the DOD that used to be part of the Department of Transportation. Generally involved in missions including:
Drug Stopping/Seizure
Envoironmental Protection
Search and Rescue
Homeland Defense
I consider this to be a pretty valuable asset of the US military, but often wonder why it hasn't been incorporated into our Navy.