Army officials would only confirm that the unit received deployment orders, refusing to say where or when the troops would move out.
About 12,500 troops of the 4th Infantry (Mechanized) Division have also received orders at Fort Hood, the nation's largest Army post.
"This repositioning of forces provides increased military capabilities in the ongoing war on terror," a Fort Hood statement said. "Any further employment of those forces deploying in a future combat role is a presidential decision."
Two 1st Cavalry units -- the 1st Battalion, 227th Aviation Regiment and the 68th Chemical Company -- received their deployment orders earlier.
Maj. Gen. Joseph Peterson commands the 1st Cavalry, often called "The First Team." Abrams tanks, Bradley fighting vehicles, and Apache and Longbow attack helicopters are the heavy weaponry of the fast-moving unit with a storied past.
In the Vietnam War, the 1st Cavalry Division introduced a new kind of warfare using Huey helicopters to quickly move combat soldiers over the jungles. The modern division is "digitized" with computers linking its arsenal of tanks and attack helicopters.
The 1st Cavalry was formed in 1921 at Fort Bliss in West Texas, but some of its units have histories that stretch back to the Civil War. The divisional flag carries campaign streamers from Bull Run, Antietam, Gettysburg and the Wilderness.
After the Civil War, units were deployed to the West where they fought Arapahos, Comanches, Sioux and Apaches. In one battle, Col. George Armstrong Custer and his 7th Cavalry Regiment were wiped out in 1876 on the Little Big Horn River.