Defcon Level September 11th, 2001: Attack On The Twin Towers
Defcon 3 was reached on September 11th, 2001, or 9-11 after two hijacked planes flew into the world trade center towers, also known as the twin towers. One plane flew into the Pentagon and a fourth intended for Washington D.C. crashed into a field in Pennsylvania.
The 9/11, or September 11th, 2001 twin tower attacks killed 2,996 people making it the deadliest terror attack on US soil in history. The Secretary of Defense issued an order on 9/11 to raise the alert level to Defcon 3 with the possibility of raising the alert level from defcon 3 to defcon 2 but, but level 2 was never reached after the September 11th terrorist attacks were carried out.