'Stealth helicopters' used in Bin Laden raid

The US forces who raided the safehouse of Osama Bin Laden appear to have caught him completely by surprise - and to have avoided detection by Pakistani radar. How did they do it?

One answer, experts believe, is that the special operations team used previously unseen stealth helicopters.

1. Silver finish makes it harder to detect on radar and by infrared sensors
2. Shape of tailboom has been altered and possibly enlarged to evade radar
3. Pan-like cover or hubcap over the rear rotor head conceals exposed machinery which is more easily picked up on radar
4. Extra blades on tail rotor reduce noise and lessen typical chopper sound
Rest of aircraft: There is speculation that the main rotor could also have had extra blades, retractable landing gear and a cover over the main rotor head
Source: Aviation Week

The evidence for this comes from images of the wreckage of one of the helicopters, which departing Seals destroyed after it crash landed in the compound.

The tail of the top secret aircraft survived, providing a treasure chest of clues for aviation experts.
After some detective work, these experts have concluded it was a UH-60 Blackhawk, heavily modified to make it quieter and less visible to radar.
They are confident the raid marks the first time that a stealth helicopter has been used operationally.
It wouldn't be the first of its kind in existence, however. Sikorsky Aircraft built a number of prototype stealth helicopters, known as the RAH-66 Comanche, for the US Army. The programme was cancelled in 2004, due to escalating costs, before the helicopter become operational.

The RAH-66 Comanche had some stealth technologies
"What's new here is this was operational use," says Bill Sweetman, editor of Aviation Week. "We really haven't seen stealth helicopters used in this way before.
"The bottom line is about increasing the element of surprise. The less warning that the target has the better."
In this kind of situation an escape route for the aircraft might be needed, he adds, in which case time is of the essence.
To make a helicopter stealthy, you have to get rid of certain shapes and areas that are easily picked up on radar, says Tony Osborne, deputy editor of Rotorhub, a UK-based helicopter magazine
The RAH-66 Comanche had some stealth technologies
"What's new here is this was operational use," says Bill Sweetman, editor of Aviation Week. "We really haven't seen stealth helicopters used in this way before.
"The bottom line is about increasing the element of surprise. The less warning that the target has the better."
In this kind of situation an escape route for the aircraft might be needed, he adds, in which case time is of the essence.