The U.S. military is providing more than 30,000 troops to help with security during Tuesday's presidential inauguration and to be ready to respond to any emergency.  

About 18,000 troops will have specific jobs to help police deal with the millions of people expected to flood into downtown Washington to see the inauguration ceremony and parade. They will provide such services as communications, healthcare and transportation by land, air and on the Potomac River. The military will also provide bomb-sniffing dogs, explosives disposal units and teams to deal with any release of radiation, or chemical or biological toxins.

Local police have such capabilities, but need more of them during an event of this magnitude.

Pentagon Spokesman Bryan Whitman says another 14,000 troops will be on stand-by status in and near the city, ready to respond to any emergency.

"In the unlikely event that there should be some sort of crisis that requires some sort of consequence management, we will have the forces and the skills readily available to assist law enforcement [authorities] in any type of activity like that," he said.

Under U.S. law, active-duty troops cannot engage directly in domestic law enforcement, so the majority of the troops on duty in Washington on Inauguration Day will be from the National Guard. The Guard works under the authority of state governors, and is allowed to do law enforcement in special circumstances.

In addition to the troops on the ground, Whitman says the military will provide what he called "active deterrence," including combat air patrols over the city and control of the region's airspace.