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New top-secret stealth choppers used on bin Laden raid

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The US special-ops troops who killed Osama bin Laden at the weekend appear to have travelled to their target in previously unknown stealth helicopters. One of the secret choppers was disabled during the raid and blown up by the departing SEAL commandos in a largely successful attempt to prevent its technology falling into non-US hands, but surviving fragments of the tail offer intriguing clues as to the aircraft's design.

Photos published by the Daily Mail from the scene of the raid show the surviving tail assembly of the wrecked copter – the rest of the aircraft appears to have been successfully destroyed by the US troops before they left. It appears that the helicopter may have been a highly modified version of the Sikorsky H-60 Blackhawk, a standard helicopter widely used by the regular US forces. The special-operations command is known to use modified and upgraded variants of the H-60, though none seen until now were as comprehensively altered as this.

The secret copter appears to feature extra blades on the tail rotor, which would allow it to fly significantly less noisily than a standard Blackhawk. The complex tail-rotor hub, which would normally reflect back a lot of radar, is covered by a pan-like assembly which would offer some stealth benefits, and the tail boom itself as well as the stabiliser planes attached to it have been altered from those seen on a standard Blackhawk in a way which would reduce the aircraft's radar signature further.

According to experts at Aviation Week, the paint finish is a "silver loaded finish". This is designed not to reduce radar signature but rather to make it harder to detect the helicopter using infrared sensors – either those in a fixed search-and-track network or, more likely in this context, those found in the seeker heads of portable anti-aircraft missiles.

Thanks to the demolition work carried out by the departing SEALs, it is impossible to know what other mods had been carried out on the wrecked chopper. However it is likely to have had extra blades on its main rotor head and other features intended to cut down on noise. There will also, probably, have been major efforts to manage the hot engine gases in such a way as to make the copter's exhaust plume cooler and less easily picked up by infrared sensors.

Radar reduction measures will also have been present, but it is much harder to cut down a helicopter's radar cross-section than an aeroplane's and the designers' primary focus is likely to have been more on infrared and especially on noise. The specially-pimped secret specwar copter will still in all likelihood have made a terrific racket if one were standing next to it: but bin Laden's compound guards will not have heard it until it was much closer than a normal H-60 could have reached undetected, so cutting down on the time from warning to arrival.

The radar aspect of the mission will have been much less important than noise and infrared. A somewhat-lessened radar signature might have helped in allowing the US aircraft to transit through Pakistan's central airspace without causing a diplomatic row before they'd even arrived: flying low will probably have helped more. But one should also note that there are routine procedures already in place for secret US flights over Pakistan, which allow, among other things, for the extensive CIA drone airstrike assassination campaign in the northwestern border areas. Given the routine presence of large numbers of US aircraft on secret missions over Pakistan on any normal day, the raiding force would probably not have caused any alarm to Pakistani military radar operators until almost at their target, even without any stealth.

Quite apart from the helicopters used in the actual raid, other aircraft are sure to have participated in the operation – both to provide overhead video surveillance and to relay reliable high-bandwidth communications from the ground units into the US military's worldwide grid and thence back to Washington for the President and his staff. It is possible to do this without relay aircraft overhead by using satellite communications, but the SEALs and their helicopter support won't have had the time or inclination to be faffing with dishes.

Rumour has it that the recently disclosed but still highly secret RQ-170 stealth drone – aka "the Beast of Kandahar" before it was finally publicly avowed by the US Air Force – may have been involved in the comms'n'video top cover mission. ®

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