NORAD is unique in the world. It really is a bi-national command. For example, it has happened that US Air Force F-15s could not fly because of an accident.
They grounded their whole fleet.
We put Canadian F-18s into Alaska region to stand alert for them. So there are occasions, such as Operation Noble Eagle, for example.
It's not inconceivable that you would have a civilian aircraft begin in Canadian airspace and pose a threat, a 9/11 scenario. We practise that binational work regularly. I'm one of the authorities on that, and I'm trained regularly in scenarios in that regard.
The cross-border doesn't happen very often. I have the exact numbers. I've read some of the testimony before the committee, and I can tell you that in 15 years, the Americans crossed our border with armed fighters four times, and Canada crossed their borders six times. I'm not sure of the numbers that you may have heard previously, but that is fresh off the press, because I anticipated that question, based on some of the previous ones you've had.