Well here is a pic of one:
http://www.army.mil/cmh-pg/books/Vietnam/Engineers/pic-98.jpg
http://www.army.mil/cmh-pg/books/Vietnam/Engineers/ch7.htm
see sec 98
and another
http://www.fao.org/docrep/x5394e/x5394e16.jpg
http://www.15thengineer.50megs.com/M_ROTH.HTM