Hi,
I just took my first stab at Icon editing, and I've created an icon for the US Patrol Air Cushion Vehicle, an armed hovercraft used by the US Navy and the US Army's 9th Infantry Division in Vietnam. The unit #491 in the USMC OOB, and uses Icon# 1858.
The files can be downloaded here:
http://www.3commando.org/images/Obat013.obf
http://www.3commando.org/images/Icon0090.shp
Please let me know what you all think!