Nationwide drills test readiness plans.

The largest national terrorism exercise in history showcased new plans and structures to react to large-scale attacks on the United States.

The third Top Officials event, or TOPOFF, that ended in April involved more than 10,000 participants from more than 200 federal, states, local, private sector and international organizations. The event took the Department of Homeland Security two years to plan.

TOPOFF-3 featured two inaugural performances. Authorities implemented the recently issued National Incident Management System and National Response Plan. "We took these two cars off the showroom floor, and we took them on a very, very challenging test ride," noted one senior Department of Homeland Security official during a background briefing.

The exercise began during the first week in March, with an intelligence and information portion meant to test agencies' abilities to share information up and down the chain of command. Those intelligence nuggets pointed to a series of preventable terrorist acts. If coordination among state, federal and local partners were successful, the number of simulated attacks would be reduced. Officials noted that some attacks were thwarted during the exercise, but are saving details for after-action analysis.

For the simulations sake, other attacks could not be prevented-namely two weapons of mass destruction attacks that "killed" thousands of citizens.

The National Incident Management System and National Response Plan both will be changed to reflect lessons learned. "We're anxious to continue tweaking those documents now," the official said. "We have the baseline documents that we're now going to build standard operating procedures and operational supplements."

Under the systems, any unmet requirements from the state and local level come into a joint military field office, where the federal agency partners determine if they can provide a solution to the problem.

"We built in some deliberate Defense Department play in this exercise, some of it in coordination with the state National Guard units, to figure out who might have the best capability and be able to best respond," the senior DHS official noted.

After-action comments also addressed an often-cited problem to reacting to a massive attack the lack of hospital space to handle the surge in wounded. One of the Pentagon's roles in the aftermath of a massive weapon strike would be setting up mobile hospitals. Another military role centered on airlifting critical patients out of the attack zones for treatment.