A helicopter was shot down today by Afghan insurgents as it was rushing to aid troops in a firefight, killing 30 Americans, including 22 Navy SEALs, most of whom belonged to Team 6, the unit whose members were involved in the raid that killed Osama bin Laden, U.S. officials said. It's unclear how far away the helicopter was from the initial firefight when it went down and unclear how the troops in the firefight got to the crash location, the official said. Although the Taliban have claimed to have shot the helicopter down, U.S. officials have only identified the attackers as insurgents. The last worst one-day U.S. casualty record in Afghanistan was on June 28, 2005 when 16 U.S. soldiers were killed in Kunar province after a helicopter was shot down by Taliban insurgents.