Black Hawk down. Well, not quite.

The helicopter that failed and was blown up by U.S. special forces after the raid that killed Osama bin Laden was a never-before-seen stealthy design, and presumably top-secret, leaving aviation and military analysts both mystified and fascinated.

The only parts that survived were its smoothed tail, apparently coated with radar-defeating reflective surfaces, and a five- or six-bladed tail rotor, designed to minimize noise and radar signature.

Applying stealth and noise-reduction technologies to helicopters is difficult because long, whirling rotor blades are ideal for creating a big radar reflection. But various designs for stealth helicopters have emerged in recent years. Some analysts suggest this helicopter was a much-modified Black Hawk, a type already in the special forces inventory.

The tail was last seen being hauled away by a Pakistani with a tractor. The Pentagon will want it back. No doubt Chinese and Russian military experts would pay dearly to have a look.

For web readers, click on the infographic link at left for a detailed look at the stealth chopper.