The rusted shell of an old passenger jet sat out in a field, its tail broken off. Good for hijacking practice, U.S. Marines speculated Sunday as they examined an Iraqi training base about 20 miles south of Baghdad.

The Americans also found a full obstacle course -- with wooden walls and other barriers to be climbed over or crawled under -- as well as a three-story concrete tower draped with ropes, apparently for rappelling.

President Saddam Hussein's regime has said the camp, part of a larger military reservation in a bend of the Tigris River, was used for anti-terrorism training for Iraqi special forces.

But U.S. officials and others have long suspected the camp trained terrorists. Two former Iraqi military officers told The New York Times and PBS' Frontline in the fall of 2001 that Iraqis and non-Iraqi Arabs were brought here to practice hijacking planes and trains, planting bombs and staging assassinations.

U.N. inspectors looking for biological weapons reported seeing a plane there. The defectors said the plane was a Boeing 707. The one seen on Sunday was not.

Another part of the base was Saddam's main biological weapons center before the first Gulf War, the U.N. inspectors learned in the 1990s. They said about 10 scientists and 100 other people worked on developing ways to deliver anthrax, ricin and other deadly substances over wide areas.

The Republican Guard 2nd Corps headquarters also is nearby, and some intelligence experts have said another camp trained young members of the Fedayeen Saddam militia in assassination, sabotage and espionage.

The military reservation sprawls next to Salman Pak, a town named for a 7th century Persian convert to Islam who was the prophet Muhammad's barber. Salman Pak, which means "Salman the Pure" in Farsi, died in the region and a shrine to him in the town attracts many Muslim pilgrims.

In attacking the military base, the Marines kept away from the nearby ruins of Ctesiphon, a Persian capital -- its main architectural wonder, the 3rd century, 99-foot-high arched dome of King Sapor's great banqueting hall, still standing.

Hours after Marines occupied the base Sunday morning, a tour of the suspected terrorist training compound found a series of curious sights.

Plastic chairs were bolted to the ground facing each other, creating a kind of classroom in a clearing in the woods. A nearby storehouse was filled with gas masks, Baath Party plaques and bright orange rappelling gear. Farther along, speedboats lay beached in the shade of a tree.

The passenger plane's sun-bleached fuselage lay alone in a large, barren field. A fire engine sat at one intersection. Elsewhere, the twisted metal wreck of a double-decker bus stood near three decrepit green and red train cars.

At U.S. Central Command in Qatar, Brig. Gen. Vincent Brooks said Marines raided the complex using information obtained from captured foreign fighters of various nations, including Egypt and Sudan.

"The nature of the work being done by some of those people we captured, their inferences about the type of training they received, all these things give us the impression that there is terrorist training that was conducted at Salman Pak," Brooks said Sunday.

He said the camp was "just one of a number of examples" of such training activity found in Iraq by coalition troops. "It reinforces the likelihood of links between this regime and external terrorist organizations," he said.

The base was deserted when the Marines got to it Sunday morning after bombing and shelling it through the night. The artillery barrage turned one field into a blackened moonscape.

A large hole, presumably from a laser-guided bomb, pierced the ceiling and the floor of one of the buildings. A group of tired Marines slept on couches and beds abandoned in a nearby room, while others searched through the buildings.

After intelligence officers finished searching the training camp, Marines began stuffing boxes and plastic bags with military IDs, pickaxes, Qurans, old uniforms, gas masks and a couple of soccer uniforms.

"It looks like guys are coming back from the shopping mall," said Capt. Glenn Van Airsdale, a helicopter pilot from Neenah, Wis.