In an attack that could have been easily prevented had the headquarters command post been on their toes, the VC's breach their airfield's perimeter and attack headquarters in the middle of the night. By morning, the fighting is over, but several important planes have been destroyed.
Perhaps a bit too much resting and too many Liberties and movies in the dark have lulled the American soldiers into a fall sense of security. The old "they can't touch us" mentality has returned, and the VC targeted in on it. With one swift attack, the enemy crumbles the American's wall of safety, and the soldiers are left to pick up the pieces of their mistake.
This sense of security is reminiscent of the feeling that so many of Caputo's men had felt.....