AL AMARIYAH, Iraq (Oct. 23. 2005) -- The convoy of assault amphibian vehicles came up on a cluster of houses here during an operation late last summer. After cordoning off the area with the tracked vehicles, infantrymen dismounted from the armored vehicles, providing another level of security for the ‘cordon and knock’ operation. The AAVs—labeled ‘green dragons’ for their size and loud engines by local Iraqis—were positioned on a defensive perimeter and their Marine crewmen kept watch as infantrymen began going house-to-house collecting information and searching for illegal weapons. Assault amphibian vehicles are huge, ungainly war machines called “tracks” or...