Six U.S. troops killed in chopper crash in Afghanistan

Six Americans were killed when their Blackhawk helicopter crashed in southern Afghanistan.

The Blackhawk, with 7 aboard, was one of two American helicopters on a daytime mission in southern Afghanistan when it was forced to make a crash landing. What caused it to go down is still unknown but the second chopper saw no sign of enemy fire.

Initial reports reaching the Pentagon said the crew of the downed aircraft did come under fire as they tried to get out of the helicopter.

But military officers in Afghanistan have since discounted those reports. Exactly how those six Americans died remains unclear. One thing is certain --  by the time a rescue force could get there, only one aboard was still alive.

The loss of six Americans was a grim reminder that while their role has switched from combat to training and advising Afghan forces, U.S. troops are still in harm's way.

 It was the worst single day loss for the U.S. in the six months since Afghan troops officially took the lead in combat operations.

Still, U.S. losses are down dramatically -- 125 so far this year compared to 310 last year, and a high of 499 in 2010 at the height of the fighting.

Casualties have gone down as the number of American troops has gone down from a high of 100,000 to the current 42,700.

Then there's the financial cost.  To date, the Pentagon has spent more than $500 billion on the war in Afghanistan. A defense spending bill the Senate is expected to pass this week would add another $80 billion to that.