What is the Washington Navy Yard?

The Washington Navy Yard is a former shipyard and ordnance plant of the U.S. Navy in Southeast, Washington, D.C.

It is called the oldest shore establishment of the U.S. Navy, operating since the first decade of the 19th century.

It is the headquarters for the Chief of Naval Operations, Naval Sea Systems Command, Naval Historical Center, the Department of Naval History, the U.S. Navy Judge Advocate General's Corps., Naval Reactors, Marine Corps Institute and the U.S. Navy Band.

It has played key roles in U.S. history. In the War of 1812 and the Civil War, the Navy Yard was a key link in the defense of the capital. President Lincoln was a frequent visitor.

By World War II, the Navy Yard was the largest naval ordnance plant in the world. The weapons built there were used in every war in which the Unites States fought until the 1960s, according to the Naval History and Heritage Command.

On Sept. 16, 2013, gunman Aaron Alexis fatally shot 12 people and injured three others in a massacre at the headquarters of the Naval Sea Systems Command.

It was the second deadliest-mass shooting on a U.S. military base, behind the Fort Hood, Texas, shooting in 2009.

Alexis was killed by police.