But there’s a growing belief that other stealthy choppers might have been present, as well. It’s the latest in a series of  revelations regarding the sophisticated tactics and techs behind the high-stakes raid.

We know about the pair of radar-evading Blackhawks because one of the elusive birds — dubbed “Silenthawks” by the media — crashed inside the bin Laden compound, leaving behind an intact tail rotor that photographers documented the following morning, and which aviation geeks used to infer the aircraft’s overall configuration.

That crash, plus the dicey politics surrounding the CIA-led assault, offer up circumstantial evidence of an even more secretive “silent” helicopter: a possible variant of the twin-rotor MH-47 Chinook, sporting the same stealth treatments as the Silenthawk and operated by the same 160th Special Operations Aviation Regiment.

As he did with the Silenthawk, aviation journalist David Cenciotti commissioned artist Ugo Crisponi to produce concept art depicting this alleged copter. (See artwork, above.)

Early reporting, including our own, proposed that Chinooks likely participated in the raid, for purely mathematical reasons. Twenty-four Navy SEALs and one dog would max out the capacity of a pair of H-60s. A single H-47, never mind two, could carry the whole assault force with room to spare.

That assumption was challenged on May 3, when CIA chief Leon Panetta said the assault birds were definitely “Blackhawks.” The same day, the photographic evidence surfaced of those choppers’ special mods. From that, observers concluded that the operation was conducted without Pakistani approval, and indeed against their wishes, using H-60 helicopters capable of slipping past Islamabad’s radars.

That seemed to definitively rule out the big, loud, radar-reflecting Chinooks. “I don’t believe that ‘normal’ MH-47s were involved,” Cenciotti wrote on May 6, owing to “considerations on the stealthiness of the formation.”

Then, this week, off-the-record government sources told the AP that three Chinooks indeed supported the Abbottabad operation, as a reserve force. The schoolbus-size aircraft — normally used to haul platoons in Afghanistan’s mountains — “land[ed] in a deserted area roughly two-thirds of the way to bin Laden’s compound.”

The reserve choppers carried two dozen reinforcement Navy SEALs, in case the original assault team needed rescuing. With room for around 40 troops in each craft, that left plenty of room for the back-up Chinooks to exfil the SEALs in the compound — a contingency that proved necessary when one of the Silenthawks went down.

Cenciotti connected the dots, from the need for stealthiness to the confirmed presence of H-47s. “I believe that there must be also a modified MH-47 flying with the 160 SOAR,” he concluded on May 18. “Unlike the Blackhawk, we have no photographic evidences of it, but I think that their existence is somehow confirmed … ”

It’s plausible. Sikorsky, maker of the Blackhawk, surely had a hand — alongside the Army and Lockheed Martin — in producing the Silenthawk, perhaps relying on techniques it refined while developing the now-canceled RAH-66 Comanche stealth scout copter. Boeing, which manufactures the Chinook, was Sikorsky’s partner on Comanche, and has since used that chopper’s heat-absorbing paint on its own V-22 Osprey tiltrotor.

That said, the stealthy Chinook is by no means a certainty. It’s possible that the reserve force, trailing behind the attackers, had less need for stealth while approaching Abbottabad. But considering the cascade of amazing tech that has emerged from the hit on bin Laden, a radar-evading heavylift chopper would hardly defy belief.