If you compare an overhead picture of the Pentagon today with one from 1943, they’ll look pretty much the same, aside from some obvious changes to the adjacent roads and grounds. But nearly all of what people see when they look at the Pentagon today didn’t exist when the building was completed in 1943.
Officially, the Pentagon Renovation Project (PenRen) is recorded as being carried out from 1998 to 2011, but the building underwent changes almost immediately after it was built. The wide-open office bays, built to take advantage of cross-ventilation via open windows, were carved into warrens of enclosed private offices. Service corridors and walkways were sealed off and converted into office and storage space. With passage of the National Security Act of 1947, the building became a headquarters not only for the Army, but for the Air Force and Navy as well, with each service branch eventually occupying its own wing and making its own functional modifications. Internal spaces were altered to accommodate the Joint Chiefs of Staff and the National Command Authority.

Changes were implemented piecemeal over the decades. A 100-by-100-foot helicopter pad was built on the lawn in 1955, a peak in Cold War tensions, to enable the emergency evacuation of top-ranking officials. Helicopter transport soon became a means of official transportation to and from the building, handling, in the words of Pentagon historian Alfred Goldberg, “hundreds of flights a month. A control tower was added in April 1959.”

In 1977, when the Washington Metro rail system completed a line to the Pentagon, the old underground bus lanes were replaced by an above-ground terminal that brought buses within less than 10 feet of the building on the Concourse side, and an escalator from the new Metro station brought passengers directly into the Pentagon and its underground shopping center.

Many of these changes hampered the functionality of the building’s interior spaces, and a few created security risks that became increasingly obvious as the Pentagon approached its 50th anniversary. Efforts to improve or upgrade some of the building’s internal systems were also implemented piecemeal. When renovation became an object of serious discussion in the late 1980s, the Pentagon had not met the National Electrical Code standards since 1953, and averaged 20 to 30 power failures a day. In 1989, the coal-fired utilities plant, located in a separate building, had quit working entirely, and was replaced by several rented boilers and chillers that cost $200,000 a month to run.

By the 1970s, many other Pentagon features were out of compliance with federal laws. The only elevators available to employees with disabilities were the freight elevators, which had vertically operated doors that tended to knock people on their heads. The building contained an estimated 58,000 tons of asbestos-contaminated material, along with several other hazardous materials that violated environmental and workplace safety codes. Because the use of steel had been minimized during construction, pipes were made from concrete or cast iron. Much of the building’s plumbing had become brittle and corroded. The marshy soil on which the Pentagon had been built was sinking; some parts of the basement had dropped nearly a foot since 1943.

The deterioration reached a crisis point recounted by author Steve Vogel in his book The Pentagon: A History. On the evening of Aug. 7, 1990 – the day the military launched Operation Desert Shield and began moving troops and flight squadrons into the Middle East to counter Saddam Hussein’s invasion of Kuwait – a smoking coffeepot in the Joint Chiefs’ area triggered fire alarms, which brought Arlington County firefighters to the scene. When the firefighters connected their truck to a standpipe and pressurized the system, an old 10-inch pipe blew apart in one of the underground steam tunnels. Chaos ensued. Vogel wrote: “A torrent of muddy water began pouring into the Pentagon basement . . . Water was cascading down the hallways and spraying violently out of a crawlspace … Hundreds of thousands of gallons of water – eventually millions of gallons – poured into the building.”

The rising water approached a high-voltage electrical vault, and for a frightening interval electricians feared they might have to cut power to half the building just as U.S. forces were inserting themselves into Saudi Arabia. The flood was brought under control, but the point many had been trying to make for years – most notably David O. “Doc” Cooke, the civilian director of administration and management known informally as “The Mayor of the Pentagon” – could no longer be denied: The disintegration of the Pentagon was an urgent national security issue.