I also need to print a retraction. The DEFCON system was created in 1959, not 1993.
DEFCON 2
Cuban Missile Crisis
During the Cuban Missile Crisis on October 16–28, 1962, the U.S. Armed Forces (with the exception of United States Army Europe (USAREUR)) were ordered to DEFCON 3. On October 24, Strategic Air Command (SAC) was ordered to DEFCON 2, while the rest of the U.S. Armed Forces remained at DEFCON 3. SAC remained at DEFCON 2 until November 15.
Persian Gulf War
On January 15, 1991, the Joint Chiefs of Staff declared DEFCON 2 in the opening phase of Operation Desert Storm during the Persian Gulf War.
DEFCON 3
Yom Kippur War
On October 6, 1973, Egypt and Syria launched a joint attack on Israel resulting in the Yom Kippur War. The United States became concerned that the Soviet Union might intervene, and on October 25, US forces, including Strategic Air Command, Continental Air Defense Command, European Command and the Sixth Fleet, were placed at DEFCON 3.
According to documents declassified in 2016, the move to DEFCON 3 was motivated by CIA reports indicating that the Soviet Union had sent a ship to Egypt carrying nuclear weapons along with two other amphibious vessels. Soviet troops never landed, although the ship supposedly transporting nuclear weapons did arrive in Egypt. Further details are unavailable and remain classified.
Over the following days, the various forces reverted to normal status with the Sixth Fleet standing down on November
Operation Paul Bunyan
Following the axe murder incident at Panmunjom on August 18, 1976, readiness levels for US forces in South Korea were increased to DEFCON 3, where they remained throughout Operation Paul Bunyan.
September 11 attacks
During the September 11 attacks, Secretary of Defense Donald Rumsfeld ordered the DEFCON level be increased to 3, and also a stand-by for a possible increase to DEFCON 2. It was lowered to DEFCON 4 on September 14.
I can't understand why we didn't go to DEFCON 2 during the Yom Kippur War.