(CNN) -- The Washington Navy Yard is the home to high-level naval personnel and is the workplace for at least 3,000 service members and civilian employees. Located in the heart of Washington, D.C., the premises include a park and many buildings.
Chief of Naval Operations Jonathan Greenert was at his residence at the Yard on Monday and was evacuated, CNN's Barbara Starr said.
She added that in her experience visiting the facility, security is extensive. Everyone must have clearance to be there or valid identification that allows them entry.
But she added that "you could have all the authority in the world to be on the installation" and still plan to do harm without detection by guards.
The Yard includes the headquarters for the Naval Historical Center and the U.S. Navy Judge Advocate General's Corps, among others. It's the headquarters for the Naval Sea Systems Command, where police said shots were fired Monday.
Capt. Mark Vandroff spoke to reporters, explaining that he and his colleagues remained in a conference room in their building -- 197 -- hunkered down until the scene was safe.
He described the building as the largest of three overseen by the Naval Sea System command, the Navy's organization that procures and maintains ships and submarines. Building 197 houses headquarter staff, legal team, contractors, engineers and buyers of various weapon and defense systems, among others, he said.
Vandroff added that he was very happy that his staff remained calm, though they were scared as they hunkered down in a conference room. "'Cause we knew if we sheltered in place eventually the police would come get us," he said.
The Yard has a dramatic history, its website says.
A former shipyard and ordnance plant, it's the oldest U.S. onshore installation.
It was added to the National Register of Historic Places in 1973 and designated a National Historic Landmark three years later.
The Yard was created in 1799 by an act of Congress, the Naval History and Heritage Command says. It was envisioned as a shipbuilding and fitting facility on the Anacostia River and over the years has serviced several storied vessels, including the USS Constitution.
During the War of 1812, the Yard burned down and was rebuilt as a weapons manufacturing hub. It has also been the scene of significant advancements in military technology. During the War of 1812, Robert Fulton conducted research and testing on his clockwork torpedo, and in 1822, Commodore John Rodgers built the United States' first marine railway for the overhaul of large vessels at the Yard, according to its site.
The Yard was crucial to the defense of Washington during the Civil War, according to its website. President Abraham Lincoln frequently visited the Yard many times, according to the Yard's site. The body of Lincoln's killer, John Wilkes Booth, was examined and identified on a ship moored at there.
Amid World War I, the Yard made Navy ordnance, including the 14-inch naval railway guns used in France in the war.
In the years after World War II and into the Cold War era, the Yard's military role lessened.