Vigilant Guardian, the semiannual NORAD exercise that had been running in conjunction with Global Guardian for several days and which postulated a bomber attack from the former Soviet Union. Vigilant Guardian is a Command Post Exercise (CPX), meaning it is conducted in offices and with computers, but without actual planes in the air. The exercise involves all NORAD command levels.[3] Out of a range of scenarios being run on September 11, 2001, one was a "traditional" simulated hijacking.[4] According to General Eberhart, after the first attack, "it took about 30 seconds" to make the adjustment to the real-world situation.[5] Because of an increased number of staff, the exercise would prove to be an enabler of rapid military response for NORAD and its NEADS component, as senior officials who were manning NORAD command centers throughout the U.S., were available to make rapid decisions.[6]