An armed yacht was a yacht

Yacht

A yacht is a recreational boat or ship. The term originated from the Dutch Jacht meaning "hunt". It was originally defined as a light fast sailing vessel used by the Dutch navy to pursue pirates and other transgressors around and into the shallow waters of the Low Countries...

 that was armed with weapon

Weapon

A weapon, arm, or armament is a tool or instrument used with the aim of causing damage or harm to living beings or artificial structures or systems...

s and was typically in the service of a navy

Navy

A navy is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake- or ocean-borne combat operations and related functions...

. Their speed and maneuverability made them useful as patrol vessels. In the United States Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

 armed yachts were typically private yachts expropriated for government use in times of war. Armed yachts served as patrol vessels during the Spanish-American War

Spanish-American War

The Spanish–American War was a conflict in 1898 between Spain and the United States, effectively the result of American intervention in the ongoing Cuban War of Independence...

 and World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. In the latter conflict, armed yachts were used as patrol vessels, convoy escorts, and in anti-submarine duties.

United States