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.
I hope that you were over enthusiatic in carrying out your orders.