[3] The exterior of the building was ringed with sandbags and soldiers, and inside corridors and hallways leading to the underground vaults were barricaded "floor to ceiling".

In the event of an unstoppable assault against the capital, plans had been drawn up for surviving U.S. Army forces to fight from three centers of final resistance, with the Treasury Building as the "citadel" of the third.

[2] Under the army's plans, troops assigned to defend the White House would fight a delaying action in President's Park to cover the evacuation of Abraham Lincoln into the Treasury vaults.

[2] In the early 1930s, a decade before the tunnel was constructed, a rumor circulated that such a passageway already existed connecting the White House to the Treasury Building.

[4] Shortly after the Pearl Harbor attack, in December 1941, construction began on a hardened bunker to the east of the White House grounds that would provide a secure refuge for the president in the event of an air raid against the capital city.

[7] As a stop-gap measure, the fortified vaults in the basement of the United States Treasury Building were converted into living quarters for the president and his family to be used if an attack came before the bunker's completion.

[5][6][8] Efforts to protect the secrecy of the East Wing bunker and the White House to Treasury Building tunnel were largely fruitless.

According to a 1996 issue of U.S. News & World Report, a 150-foot (46 m) tunnel was dug into the White House connecting the Oval Office to a location in the East Wing.