The last radio contact was an urgent appeal for help. Night was falling, a rainstorm threatening, and four Navy SEAL (search) 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 Qaeda (search) 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 Qaeda fighters also were in the region. Usama bin Laden (search) 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 (search).

It was dusk as they neared the high-altitude battlefield.

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.

Lt. Gen. James Conway, director of operations for the U.S. Joint Chiefs of Staff, described the shot as "pretty lucky."

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 onboard are thought to have died in the crash. Militants then swarmed over the wreckage.

The Chinook, when hit, had been flying alongside other choppers. Their pilots immediately informed U.S. commanders of the crash, a U.S. official said on condition of anonymity because of the sensitivity of information regarding special forces operations.

U.S. warplanes, more helicopters and forces on the ground were dispatched to the site, but they were hampered by the approaching rainstorm that lashed the mountains for 24 hours.

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.

Fears were further raised when a purported Taliban (search) spokesman, Mullah Latif Hakimi, claimed rebels had captured one of the men. But he gave no proof and U.S. officials were skeptical.

Hakimi — who also claimed insurgents shot down the helicopter — often calls news organizations to take responsibility for attacks, and the information frequently proves exaggerated or untrue. His exact tie to the Taliban leadership is unclear.

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

"We put forces on the ground, we established positions so no more enemy could enter the region. Little by little we took control of the greater area so we could reach the crash site and begin recovery operations," another military spokesman, Lt. Col. Jerry O'Hara, told The Associated Press.

U.S. officials initially said 17 people were on the chopper, but later revised it downward when they realized that one of the service members who was listed on the flight manifest did not get on the aircraft.

The bodies of the 16 — ages 21 to 40 — were recovered and flown to Bagram, the main U.S. base in Afghanistan, before being transported to Dover, Del.

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.

U.S. commanders refused to give up hope for the fourth missing service member. About 300 troops and numerous aircraft were still in the area Wednesday, searching for him and hunting "a large number" of militants, Yonts said.

"We're, of course, doing everything we can to find the last of the four SEALs. And it's a real priority, and something the president asked to get briefed on this morning," National Security Adviser Stephen Hadley said aboard Air Force One.

The U.S. military has remained tightlipped on what the commandos were doing in the area, or what happened to the men following their urgent calls for help and the helicopter crash.