Have a look at this Steve.
http://en.wikipedia.org/wiki/Marsden_Matting
Marsden Matting is standardized, perforated steel
matting material originally developed by the
United States at the
Waterways Experiment Station shortly before
World War II, primarily for the rapid construction of temporary runways and landing strips. The material is also commonly known as
Marston mats for a town in North Carolina adjacent to
Camp Mackall airfield where the material was first manufactured
[1] and used in November 1941.
[2] The material was also used in the Korean and Vietnam Wars where its common name, from its
NSN nomenclature, is
pierced (or perforated) steel planking or
PSP.