Questions arise following deadly attack on US troops

BRIAN WILLIAMS, anchor: This has been a tough couple of days. In addition to the economy and the markets, we got word over the weekend that America had lost 30 service members, including 22 Navy SEALs in Afghanistan , when their Chinook dual rotor helicopter was shot down by the enemy; the single deadliest day for US troops in that war. Tonight we're learning more about who they were, what the mission was. We have two reports, beginning with NBC 's chief foreign correspondent Richard Engel in Kabul tonight. Richard , good evening.

RICHARD ENGEL reporting: Good evening, Brian . Today, the US military released new information about the mission, but there are also now new questions. Was it really necessary? Before dawn on Saturday, a senior US military official says elite American Army Rangers launch an operation to target a Taliban leader. It's around midnight, witnesses say, when the Rangers arrive by helicopter in the Tangi Valley about 60 miles southwest of Kabul . They fight hard; a gunfight lasts 30 to 40 minutes, Taliban say, before a twin rotor Chinook helicopter is called in full of reinforcements. Onboard are mostly Navy SEALs , among America 's most highly trained, lethal and secretive troops. NATO officials say as the reinforcements arrived on the target, the helicopter is hit by a rocket-propelled grenade. Witnesses say the helicopter crashes near a riverbed. 'After it crashed, it caught fire, a huge fire. We were not able to come out during the night because the Americans were around. In the morning we saw the American bodies,' he says. Chinook transport helicopters are slow and vulnerable when they take off and land. Most defenses don't work at close range. Thirty Americans are killed on the helicopter, including 22 Navy SEALs .

ENGEL: But as details emerge, so do questions. Several military analysts with special forces experience wonder why Navy SEALs were used as backup to catch a midlevel Taliban leader in an isolated, mostly unpopulated valley.

Colonel JACK JACOBS, Retired (NBC News Military Analyst): Don't forget that the SEALs are a tier one unit. But when we use them, they better be going into an area that really justifies their use.

ENGEL: It was Navy SEALs , after all, that killed Osama bin Laden in Pakistan ; a mission far clearer, analysts say, than the one that turned out to be the deadliest attack on US troops in a decade of war. US troops here, Brian , are in the midst of a gradual drawdown. The problem is the Afghan government is not asserting control, so this country is just getting more and more dangerous.

WILLIAMS: Richard Engel starting off our coverage tonight from Kabul , Afghanistan . Richard , thanks.