Some of the 5,200 troops from Fort Carson's Third Armored Cavalry Regiment deploy for duty in Iraq.
More than 230 men and women departed from Colorado Springs Monday night.
A farewell ceremony for the troops was held last week at Fort Carson.
But the usual waving flags and yellow ribbons were missing.
The unit has suffered some of the heaviest casualties so far in the war with Iraq. Forty-five soldiers have died -- more than any other Fort Carson unit.
About 60 percent of the Third Cavalry troops are returning for their second tour of duty.