Transcript for Aug. 6, 2011: A helicopter with Navy Seal passengers shot down in Afghanistan

Good evening and we begin tonight with that headline out of Afghanistan it stunned and saddened so many of us today when we heard it. What is now the single deadliest day for US forces in that war. A military chinook helicopter was shot down in the Dark Knight east of Kabul killing thirty US troops and eight Afghans everyone on board. Among the Americans killed 22 Navy SEALs most of them from team six the elite of the elite. Fellow members of their team with the ones who killed Osama bin Laden. Tonight our team from Washington to Afghanistan reporting in and we begin here with ABC's Martha Raddatz. It is a crushing loss the most elite forces in the US military. 22. Seals killed in the fiery crash of their chinook helicopter. Along with air force and army personnel. Thirty Americans in all. Eight Afghans and a dog trained specifically for special operations. It happened last night near a Taliban stronghold in ward on a province. US forces were engaged in a firefight on the ground this year note full of seals was on its way to help. When it was shot down probably by a rocket propelled grenade an eyewitness describes the same. We were outside our rooms on the veranda the witness said and we saw this helicopter flying very low. And it was hit by a rocket and it was on fire it started coming down and it crashed just yards away from our house close to the river. Most of the 22 seals were part of seal team six that heroic unit that carried out the highly successful raid. And Osama bin Laden's compound in May but none of those who actually took part in the raid. Are believed to have been on this helicopter. President Obama in the midst of an economic crisis received a terrible word last night. US special operations teams carry out up to a dozen missions a day in Afghanistan. Three to 4000. Last year alone. Since 9/11 there have been 32 seals keel but 22 win one day is devastating. There are just 300 men in seal team six so when this one incident. More than 7%. Of the highly trained highly valuable seal teen six has perished. It's a terrible loss a terrible human tragedy. But it's also hasn't significant strategic boss for the nation as well it takes a generation. To grow with special operations warrior. A loss for the nation and a loss for a tiny and close community. That one officer said has done more for this nation and we will ever know. And I'm joined by Martha Raddatz in Washington so much loss today Martha and we know that these seals operate in such secrecy and understandably so. How does the Pentagon go without notifying the families and in doing so protecting the privacy even now. Well I'm sure they had notification teams out all night active thinking a lot about that David 22. Notification teams in just that small seal community ate more elsewhere in the nation that's just so many. And what makes this even more tragic is that it follows on the heels of that bin Laden raid where those seal family's the seals themselves. In the entire country felt such pride. But tonight as you know he's feeling such an. Martha Raddatz in Washington Martha thank you.

This transcript has been automatically generated and may not be 100% accurate.