Four small, white passenger planes sit outside a hangar here under a blazing sun, with no exterior markings save for U.S. registration numbers painted on the tails. A few burly men wearing aviator sunglasses and short haircuts poke silently around the wing flaps and landing gear.

The aircraft are Pilatus PC-12s, turboprops favored by the U.S. Special Operations forces for stealth missions precisely because of their nondescript appearance. There is no hint that they are carrying high-tech sensors and cameras that can film man-size targets from 10 miles away.

To further disguise the mission, the U.S. military has taken another unusual step: It has largely outsourced the spying operation to private contractors. The contractors supply the aircraft as well as the pilots, mechanics and other personnel to help process electronic intelligence collected from the airspace over Uganda, Congo, South Sudan and the Central African Republic.

In October, President Obama sent about 100 elite U.S. troops to central Africa to scour the terrain for Joseph Kony, the messianic and brutal leader of a Ugandan rebel group. But American contractors have been secretly searching for Kony from the skies long before that, at least since 2009, under a project code-named Tusker Sand, according to documents and people familiar with the operation.

The previously unreported practice of hiring private companies to spy on huge expanses of African territory — in this region and in North Africa, where a similar surveillance program is aimed at an al-Qaeda affiliate — has been a cornerstone of the U.S. military’s secret activities on the continent. Unlike uniformed troops, plainclothes contractors are less likely to draw attention.

But because the arms-length arrangement exists outside traditional channels, there is virtually no public scrutiny or oversight. And if something goes wrong, the U.S. government and its partners acknowledge that the contractors are largely on their own.

U.S. Africa Command, which oversees military operations on the continent, declined to discuss specific missions or its reasons for outsourcing the gathering of intelligence.

In response to written questions from The Washington Post, the command stated that contractors would not get special treatment in case of a mishap. Instead, they “would be provided the same assistance that any U.S. citizen would be provided by the U.S. Government should they be in danger.”

Perils of the job

There is precedent for the use of contractors in spying operations. The military hired private firms to conduct airborne surveillance in Latin America in the 1990s and early 2000s, with sometimes-disastrous results.

In 2003, for instance, one American was killed and three others were taken hostage by Colombian insurgents after their plane crashed in the jungle. The contractors, who were working for Northrop Grumman on a Defense Department counter-narcotics program, endured five years of captivity before they were freed in a raid by Colombian police.

Peter W. Singer, a Brookings Institution senior fellow and an expert on military contracting, said the Pentagon typically turns to the private sector for “deniability,” but he added that “it rarely turns out that way.”

“When things go bad, you can have two scenarios,” he said. “Either the contractors are left holding the bag, complaining about abandonment, or else some kind of abuse happens and they’re not held accountable because of a mix of unclear legal accountability and a lack of political will to do something about it.”

Indeed, contractors knowledgeable about the central Africa mission appear to be aware that the downing of one of their planes could have far-reaching implications.

“From a purely political standpoint it is obvious the fallout of such an incident would be immense, especially if hostile forces reached the crash site first,” Commuter Air Technology, an Oklahoma defense firm, wrote in May 2010 in response to a U.S. Africa Command solicitation to expand operations. “This could turn into a prisoner/hostage situation at worst, or at the least a serious foreign relations incident highly damaging to both AFRICOM and the U.S.”

The warning was prescient. That summer, a PC-12 surveillance aircraft operated by a New Jersey contractor as part of Tusker Sand was forced to make an emergency landing in Obo, an isolated town in the Central African Republic where Kony’s forces had terrorized the population.

On board were a handful of Americans working for the firm R-4 Inc., as well as a Ugandan military officer and a Congolese officer.

The unexpected appearance of two foreign soldiers and some Americans aroused the suspicions of tribal leaders, who had been kept in the dark about Tusker Sand by their national government. They detained the crew for several hours as they debated what to do.

“We felt like we were going to prison,” said one of the American contractors involved, speaking on the condition of anonymity to discuss a sensitive operation.

The contractor said that his group contacted State Department and United Nations officials but that they declined to intervene. It was even harder to track down Africa Command officials, whose headquarters are in Stuttgart, Germany.

“Eventually, we were able to talk our way out of it,” the contractor said. “That’s all we did over there, pay people off and talk our way out of situations.”

Dwight Turner, vice president of overseas operations for R-4, said he was not personally familiar with the incident. He confirmed that his company had been involved in Tusker Sand but declined to comment further.

A growing appetite

When Tusker Sand began in late 2009, it consisted of a single PC-12, operating out of a Ugandan military hangar at Entebbe airport. The hangar also housed a Gulfstream aircraft for the country’s president, Yoweri Museveni.

According to the contractor who worked for R-4, the presidential palace was so protective of Museveni’s plane that the Americans were required to push their PC-12 out of the hangar by hand, instead of with a tractor, to avoid inadvertent scrapes.

The U.S. military’s appetite for surveillance quickly grew. On June 11, 2010, the Africa Command participated in an “Industry Day” to drum up interest. More than 50 private contractors were invited to develop proposals to expand Tusker Sand and Creek Sand, the program aimed at al-Qaeda in the Islamic Maghreb, which operates mainly in Mali.

Unclassified documents prepared for the event show that the military wanted contractors to provide at least a combined 44 personnel for the programs, with double that number if the Africa Command decided to “surge” either one of them. At a minimum, contractors were told that they would have to keep planes flying for 150 hours a month.

Among the jobs to be outsourced: pilots, sensor operators, intelligence analysts, mechanics and linguists. The expectation was that the personnel would be veterans; most needed to certify that they had passed the military’s survival, resistance and escape training course, because of the possibility of aircrews being downed behind enemy lines.

Contractors would have to supply the surveillance gear, including electro-optical and infrared sensors that work in the dark, and a laser-emitting sensor that can peer under the jungle canopy. All had to be concealed within the body of the plane with retractable mounting to avoid attracting suspicion.

Another document stipulated that prospective firms fly “innocuous” aircraft that would “blend into the local operating area.” In a PowerPoint presentation posted on a federal government Web site for contractors, the Africa Command warned firms bidding for the work that African countries would be “uncomfortable” with activities that might look suspicious, adding: “Don’t want covert aircraft, just friendly looking aircraft.”

In addition to expanding Tusker Sand and Creek Sand, the Africa Command said it wanted to start a drone-based program, dubbed Tusker Wing, to search for members of Kony’s militia, the Lord’s Resistance Army.

That plan envisioned contractors using blimps equipped with cameras as well as ScanEagles, small and unmanned aircraft that can be launched with a catapult but stay aloft for 22 hours at a time, according to Gene Healey, a contractor who helped prepare a study for the Africa Command.

Healey said the Africa Command was initially enthusiastic about Tusker Wing but canceled the program, without explanation, before it got off the ground. Africa Command officials declined to comment.

Nonetheless, the number of manned surveillance flights for Tusker Sand has gradually increased. A new contractor, Sierra Nevada Corp., began operating PC-12 flights out of Entebbe in August.

Michelle Erlach, a spokeswoman for Sierra Nevada Corp., based in Sparks, Nev., declined to answer questions about Tusker Sand or the firm’s activities in Africa. “I cannot give any details on that,” she said.

The Africa Command declined to answer questions about the contract for Tusker Sand, saying it was “proprietary in nature.”

Allies on the Hill

Tusker Sand could soon receive another boost.

In March, Sen. James M. Inhofe (R-Okla.), one of Congress’s leading voices on Africa, issued a statement expressing concern that the U.S. military was being hindered in its efforts to track the Lord’s Resistance Army.

He called on the Obama administration to give the Africa Command “the full availability” of surveillance aircraft and equipment necessary to catch Kony and conduct other counterterrorism missions.

In an interview a month later, however, Inhofe said Africa Command officials told him that things had improved and that they were no longer being shortchanged. “I have been reassured,” he said. “I think they right now have the assets they need.”

Asked whether he had any qualms about private contractors operating spy missions on behalf of the U.S. military, Inhofe said he’d “rather not get into that.”

“They are working with contractors on these things, and I know there are a lot of people involved,” he added. “I’m just not going to elaborate on where they are or what they’re doing.”

Late last month, however, the Senate Armed Services Committee passed a measure authorizing $50 million for the Defense Department to “enhance and expand” surveillance operations to help Ugandan and other regional militaries search for Kony.

A congressional staff member said the legislators’ priority was to increase and improve the surveillance operations as quickly as possible, adding that Congress was not necessarily opposed to using private companies for the Kony manhunt.

“It’s a concern, but when you’re short on resources, it’s what you have to do,” said the staffer, speaking on the condition of anonymity to discuss sensitive operations. “It’s a permissive environment. Nobody’s getting shot at, and we’re just collecting intelligence.”

Tucked into the legislative language was a rare unclassified reference to the key role played by contractors against the Lord’s Resistance Army. The committee stated that it was “concerned” that the reliance on private firms to collect intelligence for the manhunt was “unnecessarily costly and is not meeting the needs of the supporting forces.”

The Senate panel directed the Pentagon to study “alternative contracting arrangements,” emphasizing the need for aircraft that can “loiter over areas of interest for extended periods of time.”

To avoid pilot fatigue and other problems, the Pilatus PC-12s that have been the mainstay of Tusker Sand and other manned aircraft are generally limited to six to seven hours of flying a day.

Drones, however, can stay aloft for more than 20 hours at a stretch.

Staff researcher Julie Tate in Washington contributed to this report.