A "clean sweep" for a naval vessel refers to having "swept the enemy from the seas," a completely successful mission. It is traditionally indicated by
hanging a broom

Broom

A broom is a cleaning tool consisting of stiff fibers attached to, and roughly parallel to, a cylindrical handle, the broomstick. It is thus a variety of brush with a long handle. It is commonly used in combination with a dustpan....

 from a mast or lashing it to the periscope of a submarine.

History

It is said the use of brooms in this respect originated during the 1650's, when the Dutch Admiral Maarten Tromp

Maarten Tromp

Maarten Harpertszoon Tromp was an officer and later admiral in the Dutch navy. His first name is also spelled as Maerten.-Early life:...

, after a decisive victory in the First Anglo-Dutch War

First Anglo-Dutch War

The First Anglo–Dutch War was the first of the four Anglo–Dutch Wars. It was fought entirely at sea between the navies of the Commonwealth of England and the United Provinces of the Netherlands. Caused by disputes over trade, the war began with English attacks on Dutch merchant shipping, but...

, hung a broom from his mast to indicate he had "swept the British from the seas" - his opponent Admiral Blake

Robert Blake (admiral)

Robert Blake was one of the most important military commanders of the Commonwealth of England and one of the most famous English admirals of the 17th century. Blake is recognised as the chief founder of England's naval supremacy, a dominance subsequently inherited by the British Royal Navy into...

 is said to have responded with the hoisting of a whip, indicating he would whip the Dutch into submission.

The United States Submarine Service during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 generally considered a patrol a "clean sweep" if the sub sank every target she engaged. (Individual torpedoes might miss, and convoys usually had far too many ships for all to be sunk by a single boat, but these unavoidable inefficiencies did not mar a "clean sweep.")

Recent variations

Few wide-ranging war patrols have been conducted since World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, so commanding officers have taken other opportunities to fly brooms. For example, in the year 2000 the Military Sealift Command

Military Sealift Command

The Military Sealift Command is a United States Navy organization that controls most of the replenishment and military transport ships of the Navy. It first came into existence on 9 July 1949 when the Military Sea Transportation Service became solely responsible for the Department of Defense's...

 hung a broom from the flagpole yardarm outside their headquarters to symbolize its "clean sweep" of the Y2K bug

Year 2000 problem

The Year 2000 problem was a problem for both digital and non-digital documentation and data storage situations which resulted from the practice of abbreviating a four-digit year to two digits.In computer programs, the practice of representing the year with two...

 on all the command's ships.

In 2003, under circumstances perhaps closer to the traditional context, after USS Cheyenne (SSN-773)

USS Cheyenne (SSN-773)

USS Cheyenne , the last , is the third ship of the United States Navy to be named for Cheyenne, Wyoming. The contract to build her was awarded to Newport News Shipbuilding and Dry Dock Company in Newport News, Virginia on 28 November 1989 and her keel was laid down on 6 July 1992. She was launched...

 launched her Tomahawk missiles during Operation Iraqi Freedom, her commanding officer decided that placing all missiles on target, with no duds or failures, was a modern "clean sweep."

In contrast, the commanding officers of USS Ohio (SSGN-726) in 2005 and
USS Virginia (SSN-774)

USS Virginia (SSN-774)

USS Virginia is a United States Navy attack submarine, the lead boat of her class and the tenth vessel of the Navy to be named for the Commonwealth of Virginia....

 in 2006 felt that completion of Alpha sea trial

Sea trial

A sea trial is the testing phase of a watercraft . It is also referred to as a "shakedown cruise" by many naval personnel. It is usually the last phase of construction and takes place on open water, and can last from a few hours to many days.Sea trials are conducted to measure a vessel’s...

s, indicating those vessels' basic seaworthiness, qualified them to fly the broom.