"Bank Shot" was the codename of a 50-kiloton nuclear charge hidden beneath the Octagon.
Oscar Saint-Just had the device planted in a sublevel under the complex without the knowledge of most of his advisors. One of the few who knew of it was General Rachel Speer, the officer in charge of executing "Bank Shot" should it be needed.
In 1914 PD, then Secretary of War Admiral Esther McQueen used her position in the Octagon to plan and execute her coup against Rob S. Pierre's government. After Pierre had died, and most of the Committee of Public Safety was in McQueen's hands in the Octagon, Saint-Just ordered General Speer to execute "Bank Shot". The detonation evaporated the building and the surrounding area, killing McQueen, her fellow rebels, and the rest of the Committee of Public Safety along with 1.3 million citizens of Nouveau Paris living in nearby housing blocks. (HHA3.2: N, HH9)