Question: The 2010 Pentagon shooting was an attack upon the headquarters of which U.S. department?

full_context: Document 1: Pentagon Shopping Centre: The Pentagon Shopping Centre (known locally as 'The Pentagon') is a shopping centre in Chatham in Kent. The shopping centre is located next to the Waterfront bus station which replaces the Pentagon bus station, which 80% of services use. The shopping centre contains over 70 shops and 7 leisure facilities, many high street names in fashion, homeware and food stores. There are also cafes, restaurants and a bowling alley. As is common with some other 1970's era town centre shopping centres, The Pentagon does not feature a food court or any dedicated dining area. Instead, there are various food outlets scattered throughout the centre. Built as part of the redevelopment of Chatham town centre in the 1970s, the Pentagon also features the high rise Mountbatten House office block, which has controversially stood empty or part-used for most of its history. The Pentagon, Mountbatten House and the Brook multi-storey carpark are built in a distinctive orange-red brick with grey concrete.
Document 2: 2009 shooting of Pittsburgh police officers: On April 4, 2009, a shootout occurred at 1016 Fairfield Street in the Stanton Heights neighborhood of Pittsburgh, Pennsylvania, United States, stemming from a mother and her 22-year-old son's argument over a dog urinating in the house. At approximately 7:11 a.m. EDT, 22-year-old Richard Poplawski opened fire on two Pittsburgh Police officers responding to a 9-1-1 call from Poplawski's mother, who was attempting to get the police officers to remove her son from the home. Despite Poplawski's mother telling the 9-1-1 operator that Poplawski had guns, the police officers were not told. Three police officers were ultimately confirmed dead, and another two were seriously injured.
Document 3: Virginia Tech shooting: The Virginia Tech shooting, also known as the Virginia Tech massacre, occurred on April 16, 2007, on the campus of Virginia Polytechnic Institute and State University in Blacksburg, Virginia, United States. Seung-Hui Cho, a senior at Virginia Tech, shot and killed 32 people and wounded 17 others in two separate attacks (another six people were injured escaping from classroom windows), approximately two hours apart, before committing suicide.
Document 4: Washington metropolitan area: The Washington metropolitan area is the metropolitan area centered on Washington, D.C., the capital of the United States. The area includes all of the federal district and parts of the U.S. states of Maryland and Virginia, along with a small portion of West Virginia.
Document 5: Tyler courthouse shooting: On February 24, 2005, a man shot his wife and son outside the courthouse in Tyler, Texas, then engaged police and court officers in a shootout. David Hernandez Arroyo, Sr. opened fire in front of the courthouse with a semi-automatic AK-47 rifle, killing his ex-wife, and wounding his son. A downtown resident, Mark Alan Wilson, attempted to intervene but was shot dead. Arroyo was fatally shot by police after a high-speed pursuit.
Document 6: James V. Forrestal Building: The James V. Forrestal Building is a low-rise Brutalist office building located in Washington, D.C., in the United States. Originally known as Federal Office Building 5, and nicknamed the Little Pentagon, the Forrestal Building was constructed between 1965 and 1969 to accommodate United States armed forces personnel. It is named after James Forrestal, the first United States Secretary of Defense. It became the headquarters of the United States Department of Energy after that agency's creation in 1977.
Document 7: Stabbing of Spencer Stone: Spencer Stone, a-then United States Air Force senior airman, was stabbed on October 8, 2015, in downtown Sacramento, California. Stone was stabbed by a 28-year-old California man, James Tran. The event received considerable attention in the U.S., in part that Stone helped stop a gunman on a Paris-bound train traveling from Amsterdam via Brussels two months earlier in August 2015.
Document 8: Union Army Divisions, Departments and Districts: During the American Civil War, a department was a geographical command within the Union's military organization, usually reporting directly to the War Department. Many of the Union's departments were named after rivers or other bodies of water, such as the Department of the Potomac and the Department of the Tennessee. The geographical boundaries of such departments changed frequently, as did their names. As the armies became larger Departments began to be subordinated to Military Divisions, and the Departments were often sub divided into Districts and from 1862 Subdistricts. Much information on Civil War departments can be found in Eicher & Eicher, "Civil War High Commands".
Document 9: 2012 College Station, Texas shooting: On August 13, 2012, a shooting occurred in College Station, Texas near Texas A&M University around 12:30 p.m. central time, in which multiple people, mostly police officers, were shot in a shootout. The suspect, who was shot and fatally wounded in the gunfight, was later identified as 35-year-old Thomas Alton Caffall III. Police found a Vz 58 Tactical Sporter rifle, a Mosin–Nagant M91/30 rifle with a bayonet, a .40-caliber SIG Sauer P226 pistol stolen from a police officer, and a PSL rifle with a scope in his house after the shooting.
Document 10: United States Military Academy: The United States Military Academy (USMA), also known as West Point, Army, The Academy, or simply The Point, is a four-year coeducational federal service academy located in West Point, New York in Orange County. It was originally established as a fort that sits on strategic high ground overlooking the Hudson River with a scenic view, 50 mi north of New York City. It is one of the four U.S. military service academies, and one of the five U.S. service academies.
Document 11: Pentagon Force Protection Agency: The Pentagon Force Protection Agency (PFPA) is an American law enforcement agency within the U.S. Department of Defense (DoD) charged with protecting and safeguarding the occupants, visitors, and infrastructure of The Pentagon, the Mark Center Building, the Defense Health Headquarters, and other assigned Pentagon facilities.
Document 12: United States Armed Forces: The United States Armed Forces are the military forces of the United States of America. It consists of the Army, Marine Corps, Navy, Air Force, and Coast Guard. The President of the United States is the U.S. Armed Forces's overall head, and helps form military policy with the U.S. Department of Defense (DoD) and U.S. Department of Homeland Security (DHS), both federal executive departments, acting as the principal organs by which military policy is carried out. All five armed services are among the seven uniformed services of the United States.
Document 13: 2009 Fort Hood shooting: On November 5, 2009, a mass shooting took place at Fort Hood, near Killeen, Texas. Nidal Hasan, a U.S. Army major and psychiatrist, fatally shot 13 people and injured more than 30 others. The shooting was the worst mass shooting on an American military base.
Document 14: The Pentagon: The Pentagon is the headquarters of the United States Department of Defense, located in Arlington County, Virginia, across the Potomac River from Washington, D.C. As a symbol of the U.S. military, "The Pentagon" is often used metonymically to refer to the U.S. Department of Defense.
Document 15: 2010 Pentagon shooting: On March 4, 2010, John Patrick Bedell shot and wounded two Pentagon police officers at a security checkpoint in the Pentagon station of the Washington Metro rapid transit system in Arlington County, Virginia, just outside Washington, D.C. The officers returned fire, striking him in the head. He died a few hours later the next day.
ground_truth: the U.S. Department of Defense