OPERATION NORTHERN DISTRACTION
First revealed by the Toronto Star as early as December 9 2001, Northern Vigilance was set up in the arctic with Canadian assistance. As the exercise opened, NORAD explained on September 9 that it was a follow up to Operation Northern Denial, and like it was meant “to monitor a Russian air force exercise” happening just on the other side of the North Pole.  The Russians in fact cancelled this exercise as soon as they heard word of the attack in New York.
The Northern Vigilance exercise thus drew fighters away from the East Coast that day, leaving them stationed near the Arctic Circle. One news story claimed “investigators at the September 11 Commission confirm they are investigating whether NORAD’s attention was drawn in one direction – toward the north pole – while the hijackings came in from an entirely different direction.”  I'm not sure how many fighter were there or how many of these may have been active in the defense otherwise, but there is a crucialirony here. The predecessor exercise Northern Denial indicates a desire to "deny" the Russians this attack route across the North Pole, but this curiously outdated drill, by drawing fighters and attention north, may have helped open another attack route for a different enemy on the East Coast at just the right time.
Northern Vigilance also reportedly involved radar “inserts,” blips that would look like attacking planes or other airborne objects on the attack but in reality would represent nothing. How many inserts were used, on whose screens, and inserted into which air traffic regions are all questions that remain unanswered. As it became clear an attack was underway, at 9:00 am, NORAD (officially) cancelled the exercise and erased the inserts.  But until that time at least, they couldn’t help but add to the confusion in the air.