grabbing on as it taxied and took off. four fell to their deaths or were crushed by the landing gear. it was a haunting memory of the united states' humiliating withdrawal from saigon at the end of the vietnam war. president biden had promised this would never happen. >> the taliban is not the north vietnamese army. they're not remotely compliment in terms of capability. there is going to be no circumstance where we see people being lifted off the roof of an embassy of the united states from afghanistan. it is not at all comparable. >> reporter: the u.s. military was forced to fly in thousands of reinforcements, bringing in more troops than had been in afghanistan in years. to oversee what would become one of the largest airlifts in history.