You can read the details in Mailer's Armies of the Night - "a Pulitzer Prize and National Book Award-winning nonfiction novel written by Norman Mailer and sub-titled History as a Novel/The Novel as History. Mailer essentially creates his own genre for the narrative, split into historicized and novelized accounts of the October 1967 March on the Pentagon. Mailer's unique rendition of the non-fiction novel (a form coined, at least, in 1965) was one of only a few at the time, and received the most critical attention."
This genre was later used to great success by Bob Woodward.
I was at FT Bragg in Basic Training at the time. They sent a contigent of the 82nd up to guard the Pentagon.
They weren't needed. Some Signal Corps guys told us they were at Fort Myer.
The Army surrounded the Pentagon with a line of MPs (503rd), backed up by Federal Marshals to make arrests. A line is easily breeched by a concentrated force so they had inside the Pentagon a company of Combat Engineers to handle the anticipated rush on the doors of the Pentagon. The rush came and the engineers (Company A, 91st Engineers) countered when they crashed through the doors. We were an overwhelming force and pretty much cleared the steps of everyone.
The 91st Engineer Battalion, then of Fort Belvoir, had responsibility for riot control in the D.C. area.