Don,
If I understand what you're looking for this might help.
http://www.globalsecurity.org/milita.../1984/DDWF.htm
About half way down it talks about the need to use local indigenous plows or bulldozers to keep the beaches clear and at the time the need of landing with D-5 CATs for beach clearing ops in the second or third wave of a beach assault as an option. It does discuss warm weather ops and note this is from 1984. So I would agree later they must have decided to bring them in during later waves and field attached them. Best that I can do on the quick! Hope it helps?
Regards,
Pat