I've uploaded the relevant book chapter for you. There is far more than I can include in a single comment. I encourage you to read the whole 24 page long chapter.

As it turns out, on September 11th, various agencies including NORAD, the FAA, the Canadian Air Force, the National Reconnaissance Office, and possibly the Pentagon were conducting as many as five wargame drills — in some cases involving hijacked airliners; in some cases also involving blips deliberately inserted onto FAA and military radar screens which were present during (at least) the first attacks; and which in some cases had pulled significant fighter resources away from the northeast US on September 11. In addition, a close reading of key news stories published in the spring of 2004 revealed for the first time that some of these drills were “live-fly” exercises where actual aircraft were simulating the behavior of hijacked airliners in real life; all of this as the real attacks began. The fact that these exercises had never been systematically and thoroughly explored in the mainstream press, or publicly by Congress, or at least publicly in any detail by the so-called Independent 9/11 Commission made me think that they might be the Grail.

That’s exactly what they turned out to be.

but the surface accounts I see are that it’s impact to the response was fairly minimal and may have actually increased response time since all staff were at the ready and in place when a real world shift and adjustment became necessary.

This is an outright lie by national security officials to cover their asses. It had the exact opposite effect.

From the book:

Aviation Week reported, “Senior officers involved in Vigilant Guardian were manning NORAD command centers throughout the US and Canada, available to make immediate decisions.”8 This confirmed the geographic scope of the exercise. Vigilant Guardian was played up in the press as though it had facilitated a quick- er response. It did anything but that.

That Vigilant Guardian had a direct impact on the Northeast Air Defense Sector in which all four hijackings occurred was confirmed in a December 2003 original story by NJ.com, a New Jersey-based service also summarizing all major stories published by New Jersey press outlets.

NORAD also has confirmed it was running two mock drills on September 11 at various radar sites and command centers in the United States and Canada, including air force bases in upstate New York, Florida, Washington, and Alaska. One drill, Operation Vigilant Guardian, began a week before September 11 and reflected a cold war mind-set: Participants practiced for an attack across the North Pole by Russian forces.9

The story never named the second drill, and the assertion that it was strictly a cold war-type exercise is belied by direct statements of many of the principals involved that day. The NJ.com story also raised another chilling issue.

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 from an entirely different direction.10

The National Reconnaissance Office, a joint creation of the CIA and the air force that operates US spy satellites, was also running an exercise on September 11 th. This one happened to involve a plane crashing into the headquarters of the ultra-secret agency in the Washington, DC suburb of Chantilly, Virginia, just outside Dulles International airport, the origin of Flight 77.

An Associated Press story dated September of 2002 was headlined “Agency planned exercise on September 11 built around a plane crashing into a building.”

Vigilant Guardian was a hijacking drill, not a cold war exercise

There were a number of direct quotes from participants in Vigilant Guardian indicating that the drill involved hijacked airliners rather than Russian bombers.

General Arnold had been quoted by ABC news as saying, “The first thing that went through my mind [after receiving the hijacking alert for Flight 11] was, is this part of the exercise? Is this some kind of a screw-up?”

Northern Vigilance pulled fighter aircraft away from NEADS and CONUS

I found two confirmations of this and a little more information about how extensive the deployment had been. The first, indirect and incomplete, was from NJ.com.

NORAD confirmed it had only eight fighters on the East Coast for emergency scrambles on September 11. Throughout Canada and the United States, including Alaska, NORAD had 20 fighters on alert — armed, fueled up, and ready to fly in minutes.20

A more specific confirmation had already come from NORAD itself from the Northern Vigilance website.

The North American Aerospace Defense Command shall deploy fighter aircraft as necessary to Forward Operating Locations (FOLS) in Alaska and Northern Canada to monitor a Russian air force exercise in the Russian arctic and North Pacific Ocean.21

The pieces were falling together rapidly. I remembered a story that the National Security Agency (NSA) had intercepted a message on September 10th between two al Qaeda members. CNN reported:

A message intercepted by US intelligence officials September 10 declared “The match begins tomorrow,” and another declared “Tomorrow is zero hour” — but the messages were not translated until one day after the devastating terrorist attacks.22

That conversation was between Khalid Shaikh Muhammad, the so-called mas- termind of 9/11, and Mohammed Atta, the reported lead hijacker.23 Could “match” have referred to a wargame? Honegger had suggested this in 2002. The new wargame information now made that conclusion much more attractive.

It certainly appeared that someone in authority had deliberately interfered with FAA/NORAD operations on September 11th to make sure that some of the attacks succeeded. Richard Clarke’s book, previously edited by the White House, had FAA administrator Garvey referring to as many as 11 off-course/out-of-contact aircraft. Was she saying that she couldn’t tell the wargame inserts from the real thing?

It would take only a day or two more to find damning evidence that this is probably what she meant. The fact that the CIA had been running a plane-into- building exercise simultaneously with all the military exercises made me very suspicious. The first question that leapt at me was, with all these related exercises running at the same time, who or what was coordinating them? Someone at DoD had to have a regular job of knowing all the exercises being carried out everywhere to avoid SNAFUs. That question and others would require interviews.

The source is Michael C. Ruppert. Specifically from his book Crossing the Rubicon. I'll find the exact passage for you.

This video provides a summary of the drills I mentioned (timecode 7:06).