Decisions and calculations in the simulation are deliberately kept as simple as possible, so that results are unambiguous.

Casualties are obtained by simple multiplication of casualties per weapon by the percentage of weapons that penetrate the defenses. The percentage of weapons that get through is 1 minus the defensive success rate. In other words, if the defensive success rate is 80%, and the attacker uses 100 nuclear weapons, 20 weapons get through.

About half the US population lives in the twenty largest metropolitan areas, so these are obvious targets. Cities are targeted in decreasing order of population, that is New York followed by Los Angeles followed by Chicago, etc. If a target is destroyed, the attack moves on to the next largest target.

The attacker has a choice of delivery systems, just as in real life. Therefore there are two defensive success rates, one for ballistic missiles and one for all other delivery systems. The September 11 attackers used airplanes as delivery systems; previous attackers used trucks. The attacker prefers the delivery system that is more likely to succeed.

The satellite image of North America is courtesy of the AVHRR Land Pathfinder Project, a joint effort of NOAA and NASA.

Data on the twenty largest US metropolitan areas are obtained from the US Census Bureau.

Missile and nuclear weapons capabilities are approximately as estimated by the Federation of American Scientists. Estimates of other weapons are chosen to provide a range of scenarios.

The sound effects in the attack are courtesy of CodeBrain.com.

The US organization responsible for missile defense is the Missile Defense Agency.

Additional information on missile defense is provided by the Department of Defense.

The US nuclear deterrent is primarily maintained by the US Air Force and the US Navy.

The Center for Defense Information provides good estimates of defense costs and other information.

The Federation of American Scientists provide a wealth of information on missile defense and other topics.

The Union of Concerned Scientists has been studying ballistic missile defense since the "Star Wars" program of the early 1980s.

One of the oldest organizations studying nuclear war is the Physicians For Social Responsibility.

Many components of missile defense are computer-based. Computer Professionals For Social Responsibility examines missile defense issues from a computer and software perspective.

GreenPeace has taken an active stand against missile defenses.

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