Wreckage left at the scene of the raid targeting Osama bin Laden has military experts talking about the existence of a secret U.S. helicopter.
U.S. officials have said an elite team of Navy commandos flew to bin Laden's compound in Pakistan on two Black Hawk military helicopters. But experts say photos show a helicopter unlike any known to be in use.
Aviation Week magazine reports the design of the tail section and the tail rotor appear to incorporate elements that would make the helicopter harder to detect with radar.
IHS Jane's, a publishing company that specializes in military and defense issues, also says the images show evidence of stealth technology that would have made the helicopter more difficult to hear.
And a retired special operations aviator tells the Army Times newspaper that the tail section likely came from a highly-modified Black Hawk helicopter that incorporates some of the stealth technology used on for U.S. military jets.
Officials have said one of the Black Hawk helicopters used in the May 2 raid went down due to mechanical problems. They said the commandos then destroyed the helicopter to prevent sensitive technology from getting into the wrong hands.
Senior military officials have refused to comment on the speculation that the Navy commandos used a new type of helicopter.
The United States has used the Black Hawk helicopter for about 30 years.
In 1993, Somali rebels shot down two earlier versions of the Black Hawk helicopter, killing several U.S. soldiers. The event was later memorialized in the 2001 film Black Hawk Down.
One military expert tells ABC News that the modifications made to the helicopters used in the Osama bin Laden raid are a first.
Former U.S. Defense official Dan Goure said it would have been impossible for anyone at the bin Laden compound to determine the helicopters were coming right at them until it was too late.
Some information for this report was provided by AP, AFP and Reuters.