Nato defence ministers have taken part in an unprecedented exercise to test the alliance's responses to terrorism.
Nato and the US military are undergoing far-reaching reforms
The exercise at a US Air Force base opened a two-day summit in Colorado Springs in the Rocky Mountains.
Dubbed a "study seminar", the exercise involved a crisis spreading from a fictional Middle Eastern nation called Corona in 2007, officials said.
A terrorist group threatened Europe with a weapon of mass destruction delivered by a missile in the scenario.
The aim of the exercise is to prepare the ground for deploying a Nato Response Force able to intervene in crises anywhere in the world.
The force is expected to reach a full strength of up to 20,000 troops, backed by air and naval components, in 2006.
The Colorado Springs summit brings together the defence chiefs of the 19 Nato countries and seven eastern European states invited to join their ranks.
US Defence Secretary Donald Rumsfeld has said the goal is "to be able to deal with problems in hours or days, not weeks or months or years".
The $7m exercise was aimed at testing Nato's
ability to quickly resolve political and military differences
when a crisis erupts and deploy elite units outside the alliance's historic European heartland within five to 30
Officials said it took place at the US military Joint National Integration Center, a hi-tech missile defence and space warfare facility at Schriever Air Force base.
The ministers sat at a round table in a special tent with large video screens, the officials said.
At the summit the ministers will also focus on Nato peacekeeping in the Balkans and Afghanistan.
The Afghanistan mission is a historic one, out of the alliance's normal area of interest.