Kabul, Afghanistan ? The last radio contact was an urgent appeal for help. Night was falling, a rainstorm threatening, and four Navy SEAL commandos were surrounded by about a dozen militants in rugged, wooded mountains. They needed reinforcements.

That hurried call set in motion a chain of events that would lead to the U.S. military’s deadliest blow in Afghanistan, and the greatest loss of life ever for the elite force of SEALs.

Nine days after the ambush and subsequent downing of a U.S. special forces helicopter with 16 troops aboard, U.S military officials in Kabul and Washington are starting to draw a clearer picture of what happened and have revealed some details.

The four commandos – one of whom was rescued, two killed and one who is still missing – were on a reconnaissance mission on June 28 as part of Operation Red Wing, searching for Taliban-led rebels and al-Qaida fighters in Kunar province, U.S. military spokesman Col. James Yonts said.

The eastern province has long been a hotbed of militant activity and a haven for fighters loyal to renegade former premier Gulbuddin Hekmatyar, who is wanted by the United States. U.S. officials said al-Qaida fighters also were in the region. Osama bin Laden was not said to be there – though he is believed to be somewhere along the rugged Afghanistan-Pakistan frontier.

The region’s rugged, wooded mountains are popular with militants because they are easy to infiltrate from neighboring Pakistan and have plenty of places to hide.

The SEAL team – specially trained “not only in the art of combat, but also in medicine and communications” – were attacked by a “pretty large force of enemy terrorists” and radioed for reinforcements, Yonts said at a press conference.

After the radio call for help, eight Navy SEALs and an eight-member crew from the Army’s 160th Special Operations Aviation Regiment, known as the Night Stalkers, flew toward the mountains in a special forces MH-47 Chinook helicopter.

Suddenly, militants hiding in the thick forest fired what is believed to have been a rocket-propelled grenade at the massive chopper, hitting it, he said.

Though damaged, the chopper flew on for about a mile before landing badly on a small ledge on the side of the mountain, then tumbling into a steep ravine. All 16 on board are thought to have died in the crash.

In the meantime, there was no contact from the four commandos. No one knew if they had been killed in the firefight, or had survived and escaped but were unable to radio for help, the official said.

U.S. forces finally reached the wreckage of the helicopter last Thursday, 36 hours after it went down.

Then on Saturday, a breakthrough came in the desperate search for the four commandos. A friendly tribal elder living in the nearby mountains told authorities he was caring for one of them in his house, Kunar Gov. Asadullah Wafa said. It wasn’t clear how the commando got there, he said.

U.S. forces rushed to the site and found the commando, wounded, but in stable condition. He was flown to Bagram for treatment – and a debriefing, giving military commanders the first crucial clues about what happened to the ill-fated team.

But the good news didn’t last.

On Saturday, a U.S. airstrike in the region killed as many as 17 civilians, prompting a strong rebuke by the Afghan government. The next day, U.S. troops in the area spotted the bodies of two of the commandos in a deep ravine. It took another 24 hours to recover their remains and fly them to Bagram.

It was the largest loss of Navy SEALs in a single incident since the force of about 2,400 was formed in 1962.