Erik Prince, the founder of Blackwater, has a new project.

ABU DHABI, United Arab Emirates — Late one night last November, a plane carrying dozens of Colombian men touched down in this glittering seaside capital. Whisked through customs by an Emirati intelligence officer, the group boarded an unmarked bus and drove roughly 20 miles to a windswept military complex in the desert sand.

The Colombians had entered the United Arab Emirates posing as construction workers. In fact, they were soldiers for a secret American-led mercenary army being built by Erik Prince, the billionaire founder of Blackwater Worldwide, with $529 million from the oil-soaked sheikdom.

Mr. Prince, who resettled here last year after his security business faced mounting legal problems in the United States, was hired by the crown prince of Abu Dhabi to put together an 800-member battalion of foreign troops for the U.A.E., according to former employees on the project, American officials and corporate documents obtained by The New York Times.

The force is intended to conduct special operations missions inside and outside the country, defend oil pipelines and skyscrapers from terrorist attacks and put down internal revolts, the documents show. Such troops could be deployed if the Emirates faced unrest in their crowded labor camps or were challenged by pro-democracy protests like those sweeping the Arab world this year.

The U.A.E.’s rulers, viewing their own military as inadequate, also hope that the troops could blunt the regional aggression of Iran, the country’s biggest foe, the former employees said. The training camp, located on a sprawling Emirati base called Zayed Military City, is hidden behind concrete walls laced with barbed wire. Photographs show rows of identical yellow temporary buildings, used for barracks and mess halls, and a motor pool, which houses Humvees and fuel trucks. The Colombians, along with South African and other foreign troops, are trained by retired American soldiers and veterans of the German and British special operations units and the French Foreign Legion, according to the former employees and American officials.

In outsourcing critical parts of their defense to mercenaries — the soldiers of choice for medieval kings, Italian Renaissance dukes and African dictators — the Emiratis have begun a new era in the boom in wartime contracting that began after the Sept. 11, 2001, attacks. And by relying on a force largely created by Americans, they have introduced a volatile element in an already combustible region where the United States is widely viewed with suspicion.

The United Arab Emirates — an autocracy with the sheen of a progressive, modern state — are closely allied with the United States, and American officials indicated that the battalion program had some support in Washington.

“The gulf countries, and the U.A.E. in particular, don’t have a lot of military experience. It would make sense if they looked outside their borders for help,” said one Obama administration official who knew of the operation. “They might want to show that they are not to be messed with.”

Still, it is not clear whether the project has the United States’ official blessing. Legal experts and government officials said some of those involved with the battalion might be breaking federal laws that prohibit American citizens from training foreign troops if they did not secure a license from the State Department.

Mark C. Toner, a spokesman for the department, would not confirm whether Mr. Prince’s company had obtained such a license, but he said the department was investigating to see if the training effort was in violation of American laws. Mr. Toner pointed out that Blackwater (which renamed itself Xe Services ) paid $42 million in fines last year for training foreign troops in Jordan and other countries over the years.

The U.A.E.’s ambassador to Washington, Yousef al-Otaiba, declined to comment for this article. A spokesman for Mr. Prince also did not comment.

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For Mr. Prince, the foreign battalion is a bold attempt at reinvention. He is hoping to build an empire in the desert, far from the trial lawyers, Congressional investigators and Justice Department officials he is convinced worked in league to portray Blackwater as reckless. He sold the company last year, but in April, a federal appeals court reopened the case against four Blackwater guards accused of killing 17 Iraqi civilians in Baghdad in 2007.

To help fulfill his ambitions, Mr. Prince’s new company, Reflex Responses, obtained another multimillion-dollar contract to protect a string of planned nuclear power plants and to provide cybersecurity. He hopes to earn billions more, the former employees said, by assembling additional battalions of Latin American troops for the Emiratis and opening a giant complex where his company can train troops for other governments.

Knowing that his ventures are magnets for controversy, Mr. Prince has masked his involvement with the mercenary battalion. His name is not included on contracts and most other corporate documents, and company insiders have at times tried to hide his identity by referring to him by the code name “Kingfish.” But three former employees, speaking on the condition of anonymity because of confidentiality agreements, and two people involved in security contracting described Mr. Prince’s central role.

The former employees said that in recruiting the Colombians and others from halfway around the world, Mr. Prince’s subordinates were following his strict rule: hire no Muslims.

Muslim soldiers, Mr. Prince warned, could not be counted on to kill fellow Muslims.

A Lucrative Deal

Last spring, as waiters in the lobby of the Park Arjaan by Rotana Hotel passed by carrying cups of Turkish coffee, a small team of Blackwater and American military veterans huddled over plans for the foreign battalion. Armed with a black suitcase stuffed with several hundred thousand dollars’ worth of dirhams, the local currency, they began paying the first bills.

The company, often called R2, was licensed last March with 51 percent local ownership, a typical arrangement in the Emirates. It received about $21 million in start-up capital from the U.A.E., the former employees said.

Mr. Prince made the deal with Sheik Mohamed bin Zayed al-Nahyan, the crown prince of Abu Dhabi and the de facto ruler of the United Arab Emirates. The two men had known each other for several years, and it was the prince’s idea to build a foreign commando force for his country.

Savvy and pro-Western, the prince was educated at the Sandhurst military academy in Britain and formed close ties with American military officials. He is also one of the region’s staunchest hawks on Iran and is skeptical that his giant neighbor across the Strait of Hormuz will give up its nuclear program.

“He sees the logic of war dominating the region, and this thinking explains his near-obsessive efforts to build up his armed forces,” said a November 2009 cable from the American Embassy in Abu Dhabi that was obtained by the anti-secrecy group WikiLeaks.

For Mr. Prince, a 41-year-old former member of the Navy Seals, the battalion was an opportunity to turn vision into reality. At Blackwater, which had collected billions of dollars in security contracts from the United States government, he had hoped to build an army for hire that could be deployed to crisis zones in Africa, Asia and the Middle East. He even had proposed that the Central Intelligence Agency use his company for special operations missions around the globe, but to no avail. In Abu Dhabi, which he praised in an Emirati newspaper interview last year for its “pro-business” climate, he got another chance.

Mr. Prince’s exploits, both real and rumored, are the subject of fevered discussions in the private security world. He has worked with the Emirati government on various ventures in the past year, including an operation using South African mercenaries to train Somalis to fight pirates. There was talk, too, that he was hatching a scheme last year to cap the Icelandic volcano then spewing ash across Northern Europe.

The team in the hotel lobby was led by Ricky Chambers, known as C. T., a former agent with the Federal Bureau of Investigation who had worked for Mr. Prince for years; most recently, he had run a program training Afghan troops for a Blackwater subsidiary called Paravant.

He was among the half-dozen or so Americans who would serve as top managers of the project, receiving nearly $300,000 in annual compensation. Mr. Chambers and Mr. Prince soon began quietly luring American contractors from Afghanistan, Iraq and other danger spots with pay packages that topped out at more than $200,000 a year, according to a budget document. Many of those who signed on as trainers — which eventually included more than 40 veteran American, European and South African commandos — did not know of Mr. Prince’s involvement, the former employees said.

Mr. Chambers did not respond to requests for comment.

He and Mr. Prince also began looking for soldiers. They lined up Thor Global Enterprises, a company on the Caribbean island of Tortola specializing in “placing foreign servicemen in private security positions overseas,” according to a contract signed last May. The recruits would be paid about $150 a day.

Within months, large tracts of desert were bulldozed and barracks constructed. The Emirates were to provide weapons and equipment for the mercenary force, supplying everything from M-16 rifles to mortars, Leatherman knives to Land Rovers. They agreed to buy parachutes, motorcycles, rucksacks — and 24,000 pairs of socks.

To keep a low profile, Mr. Prince rarely visited the camp or a cluster of luxury villas near the Abu Dhabi airport, where R2 executives and Emirati military officers fine-tune the training schedules and arrange weapons deliveries for the battalion, former employees said. He would show up, they said, in an office suite at the DAS Tower — a skyscraper just steps from Abu Dhabi’s Corniche beach, where sunbathers lounge as cigarette boats and water scooters whiz by. Staff members there manage a number of companies that the former employees say are carrying out secret work for the Emirati government.

Emirati law prohibits disclosure of incorporation records for businesses, which typically list company officers, but it does require them to post company names on offices and storefronts. Over the past year, the sign outside the suite has changed at least twice — it now says Assurance Management Consulting.

While the documents — including contracts, budget sheets and blueprints — obtained by The Times do not mention Mr. Prince, the former employees said he negotiated the U.A.E. deal. Corporate documents describe the battalion’s possible tasks: intelligence gathering, urban combat, the securing of nuclear and radioactive materials, humanitarian missions and special operations “to destroy enemy personnel and equipment.”

One document describes “crowd-control operations” where the crowd “is not armed with firearms but does pose a risk using improvised weapons (clubs and stones).”

People involved in the project and American officials said that the Emiratis were interested in deploying the battalion to respond to terrorist attacks and put down uprisings inside the country’s sprawling labor camps, which house the Pakistanis, Filipinos and other foreigners who make up the bulk of the country’s work force. The foreign military force was planned months before the so-called Arab Spring revolts that many experts believe are unlikely to spread to the U.A.E. Iran was a particular concern.

An Eye on Iran

Although there was no expectation that the mercenary troops would be used for a stealth attack on Iran, Emirati officials talked of using them for a possible maritime and air assault to reclaim a chain of islands, mostly uninhabited, in the Persian Gulf that are the subject of a dispute between Iran and the U.A.E., the former employees said. Iran has sent military forces to at least one of the islands, Abu Musa, and Emirati officials have long been eager to retake the islands and tap their potential oil reserves.

The Emirates have a small military that includes army, air force and naval units as well as a small special operations contingent, which served in Afghanistan, but over all, their forces are considered inexperienced.

In recent years, the Emirati government has showered American defense companies with billions of dollars to help strengthen the country’s security. A company run by Richard A. Clarke, a former counterterrorism adviser during the Clinton and Bush administrations, has won several lucrative contracts to advise the U.A.E. on how to protect its infrastructure.

Some security consultants believe that Mr. Prince’s efforts to bolster the Emirates’ defenses against an Iranian threat might yield some benefits for the American government, which shares the U.A.E.’s concern about creeping Iranian influence in the region.

“As much as Erik Prince is a pariah in the United States, he may be just what the doctor ordered in the U.A.E.,” said an American security consultant with knowledge of R2’s work.

The contract includes a one-paragraph legal and ethics policy noting that R2 should institute accountability and disciplinary procedures. “The overall goal,” the contract states, “is to ensure that the team members supporting this effort continuously cast the program in a professional and moral light that will hold up to a level of media scrutiny.”

But former employees said that R2’s leaders never directly grappled with some fundamental questions about the operation. International laws governing private armies and mercenaries are murky, but would the Americans overseeing the training of a foreign army on foreign soil be breaking United States law?

Susan Kovarovics, an international trade lawyer who advises companies about export controls, said that because Reflex Responses was an Emirati company it might not need State Department authorization for its activities.

But she said that any Americans working on the project might run legal risks if they did not get government approval to participate in training the foreign troops.

Basic operational issues, too, were not addressed, the former employees said. What were the battalion’s rules of engagement? What if civilians were killed during an operation? And could a Latin American commando force deployed in the Middle East really be kept a secret?

Imported Soldiers

The first waves of mercenaries began arriving last summer. Among them was a 13-year veteran of Colombia’s National Police force named Calixto Rincón, 42, who joined the operation with hopes of providing for his family and seeing a new part of the world.

“We were practically an army for the Emirates,” Mr. Rincón, now back in Bogotá, Colombia, said in an interview. “They wanted people who had a lot of experience in countries with conflicts, like Colombia.”

Mr. Rincón’s visa carried a special stamp from the U.A.E. military intelligence branch, which is overseeing the entire project, that allowed him to move through customs and immigration without being questioned.

He soon found himself in the midst of the camp’s daily routines, which mirrored those of American military training. “We would get up at 5 a.m. and we would start physical exercises,” Mr. Rincón said. His assignment included manual labor at the expanding complex, he said. Other former employees said the troops — outfitted in Emirati military uniforms — were split into companies to work on basic infantry maneuvers, learn navigation skills and practice sniper training.

R2 spends roughly $9 million per month maintaining the battalion, which includes expenditures for employee salaries, ammunition and wages for dozens of domestic workers who cook meals, wash clothes and clean the camp, a former employee said. Mr. Rincón said that he and his companions never wanted for anything, and that their American leaders even arranged to have a chef travel from Colombia to make traditional soups.

But the secrecy of the project has sometimes created a prisonlike environment. “We didn’t have permission to even look through the door,” Mr. Rincón said. “We were only allowed outside for our morning jog, and all we could see was sand everywhere.”

The Emirates wanted the troops to be ready to deploy just weeks after stepping off the plane, but it quickly became clear that the Colombians’ military skills fell far below expectations. “Some of these kids couldn’t hit the broad side of a barn,” said a former employee. Other recruits admitted to never having fired a weapon.

Rethinking Roles

As a result, the veteran American and foreign commandos training the battalion have had to rethink their roles. They had planned to act only as “advisers” during missions — meaning they would not fire weapons — but over time, they realized that they would have to fight side by side with their troops, former officials said.

Making matters worse, the recruitment pipeline began drying up. Former employees said that Thor struggled to sign up, and keep, enough men on the ground. Mr. Rincón developed a hernia and was forced to return to Colombia, while others were dismissed from the program for drug use or poor conduct.

And R2’s own corporate leadership has also been in flux. Mr. Chambers, who helped develop the project, left after several months. A handful of other top executives, some of them former Blackwater employees, have been hired, then fired within weeks.

To bolster the force, R2 recruited a platoon of South African mercenaries, including some veterans of Executive Outcomes, a South African company notorious for staging coup attempts or suppressing rebellions against African strongmen in the 1990s. The platoon was to function as a quick-reaction force, American officials and former employees said, and began training for a practice mission: a terrorist attack on the Burj Khalifa skyscraper in Dubai, the world’s tallest building. They would secure the situation before quietly handing over control to Emirati troops.

But by last November, the battalion was officially behind schedule. The original goal was for the 800-man force to be ready by March 31; recently, former employees said, the battalion’s size was reduced to about 580 men.

Emirati military officials had promised that if this first battalion was a success, they would pay for an entire brigade of several thousand men. The new contracts would be worth billions, and would help with Mr. Prince’s next big project: a desert training complex for foreign troops patterned after Blackwater’s compound in Moyock, N.C. But before moving ahead, U.A.E. military officials have insisted that the battalion prove itself in a “real world mission.”

That has yet to happen. So far, the Latin American troops have been taken off the base only to shop and for occasional entertainment.

On a recent spring night though, after months stationed in the desert, they boarded an unmarked bus and were driven to hotels in central Dubai, a former employee said. There, some R2 executives had arranged for them to spend the evening with prostitutes.