Afghanistan Helicopter Crash Marks Deadliest Day for U.S. Forces in 10 Years

GWEN IFILL: Next tonight, a helicopter is shot down in Afghanistan, resulting in the worst day of U.S. casualties in 10 years.

Margaret Warner has the story.

MARGARET WARNER: Attack helicopters patrolled the skies today as U.S. troops on the ground cordoned off the crash site south of Kabul. Thirty Americans, including 22 Navy SEALs, plus seven Afghan troops, and an interpreter, died early Saturday in the Tangi Valley when their Chinook helicopter was shot down apparently by a rocket-propelled grenade.

The Taliban claimed responsibility. U.S. commanders in Kabul said the SEAL force was sent to assist Army Rangers, who had come under fire by insurgents during an operation to nab a Taliban leader. The Tangi Valley lies in mountainous Wardak Province just 50 miles southwest of Kabul. U.S. forces turned over the valley's sole American outpost to Afghan forces last spring.

At the White House this afternoon, President Obama said the work of the men and their mission goes on.

PRESIDENT BARACK OBAMA: I know that our troops will continue the hard work of transitioning to a stronger Afghan government and ensuring that Afghanistan is not a safe haven for terrorists.

MARGARET WARNER: The fallen men were members of the Navy's vaunted SEAL Team Six, the same special forces unit that killed Osama bin Laden in Pakistan, though none of the same troops were involved.

In Tampa today, Adm. William McRaven, who ran the bin Laden mission, was installed as chief of the entire Special Operations Command. Defense Secretary Leon Panetta lauded the contributions of special-ops forces to the decade-long war.

SECRETARY OF DEFENSE LEON PANETTA: We know that these successes are driven by the willingness of these brave warriors to shoulder heavy burdens, to take on great risks. And, as we all know, that comes oftentimes at a very high cost.

MARGARET WARNER: This was the second U.S. helicopter shot down in Afghanistan in the past two weeks.