ISLAMABAD – A assault team that killed Osama bin Ladenlink>sneakedup on his compound in radar-evading helicopters that had never beendiscussed publicly by the United States government, aviation analysts saidAfter the raid, New York Times has reported.
The commandos blew up one of the helicopters after it was damaged in a hardlanding, but news photographs of the surviving tail section revealmodifications to muffle noise and reduce the chances of detection by radar.
The stealth features, similar to those used on advanced fighter jets andbombers, help explain how two of the helicopters sped undetected throughPakistani air defenses before reaching the Bin Laden compound inAbbottabad. The use of the specially equipped helicopters also underscoresthe extent to which American officials wanted to get to Bin Laden withouttipping off Pakistani leaders.
Analysts said the raid was a rare case in which stealth aircraft, devisedfor conventional warfare during the cold war, became critical to fightingterrorism.
Military and intelligence agencies have refused to comment about the use ofstealth aircraft in this raid. But since the Sept. 11, 2001, terroristattacks, the special forces have spared no expense in developing technologyto hunt terrorists, and aviation experts said the debris from the damagedhelicopter provided further evidence of that.
Leon E. Panetta, the C.I.A. director, has said that two Black Hawkhelicopters carried about 25 Navy Seallink>membersto the compound, where they killed Bin Laden and three other people in anoperation that lasted nearly 40 minutes.
But several analysts and executives in the helicopter industry said therear section that was left behind looked nothing like the tail of a regularBlack Hawk, a popular midsize helicopter made by Sikorsky. Rather, theysaid, it appeared that the Black Hawks had been modified to incorporatesome of the features of a proposed stealth helicopter that the Pentagoncanceled in 2004.
“They would have learned an awful lot from that, and a lot of it would havebeen relevant to a program like this,” said Richard L. Aboulafia, anaviation analyst at the Teal Group in Fairfax, Va.
Mr. Aboulafia said the changes appeared to include the addition of specialcoatings to the skin to absorb radar beams and the replacement of sharpedges on the helicopter with curved ones. The gentler curves could scatterthe reflections of other radar beams in too many directions for anair-defense system to put together a coherent picture of the plane, he said.
Bill Sweetman, the editor of a military trade publication owned by AviationWeek, reported that the damaged helicopter appeared to have five or sixblades in its tail rotor, instead of the four in a standard Black Hawk.That could have allowed operators to slow the rotor speed and reduce thefamiliar chop-chop sound that most helicopters make.
A fuel cap believed to come from the helicopter the Seal team destroyed inthe raid on Osama bin Laden.CreditWarrick Page for The New York Times
A cover on the rotor that looks like a dishpan or a hubcap in the newsphotographs may have also helped reduce so-called radar signature of thecraft, the analysts said.
Lawmakers who were briefed on the mission said the damaged helicopter hadnot malfunctioned, as initially described by senior administrationofficials. Instead, they said, it got caught in an air vortex caused byhigher-than-expected temperatures and the high compound walls, whichblocked the downwash of the rotor blades.
As a result, the helicopter lost its lift power while hovering over theyard and had to make a hard landing, clipping one of the walls with itstail. Some of the Seal members later tried to destroy the craft, presumablyto hide the secret stealth components, before boarding larger backuphelicopters that carried them to Afghanistan.
Mr. Aboulafia and Mr. Sweetman both said it was harder to quiet ahelicopter than a winged plane, given all the whirling blades.
It was not clear whether the special forces had used the stealthhelicopters in any earlier raids in Afghanistan, Iraq or Pakistanlink>’stribal areas.
Indications that stealth features were added to the helicopters suggest anextension of a technology that was created to protect American fighter jetsand bombers from sophisticated air defenses in countries like Russia andChina.
The top stealth fighter, the F-22link>,has never been flown in combat. The long-range B-2 bombers have been usedsparingly, including a recent bombing run that destroyed an airfield inLibya.
Mr. Aboulafia said the latest modifications seemed similar to plans for thestealthy Comanche helicopter, which were canceled in 2004 after billions ofdollars in cost overruns. Those plans also arose during the cold war. Butwith the lack of anti-aircraft threats in Iraq and Afghanistan, Armyofficials decided that full-scale production of stealth copters was notworth the cost.
“Stealth never made sense in an Afghan context,” Mr. Aboulafia said,“unless you were also looking at the Pakistan dimension.”
Some analysts wondered whether the C.I.A. might have also used a stealthydronelink>togather intelligence before the raid on Bin Laden’s compound and possibly tomonitor the attack.
In addition to satellite photographs, the special forces rely on Predatorand Reaper drones in Iraq and Afghanistan to provide video showing how manypeople are living in insurgent compounds and their patterns of activity.But the Predators and Reapers would be easy for almost any air-defensesystem to track.
The Pentagon announced in late 2009 that it was testing a bat-wingedstealth drone, the RQ-170 Sentinel, in Afghanistan, and it was quicklydubbed the Beast of Kandahar. Military officials have not mentioned itpublicly since then, and they would not say this week whether it had beeninvolved in the hunt for Bin Laden. New York Times