road infrastructure; a dump for supplies, ammunition, and gasoline drums, along with a drinkable water and a minimal electrical grid for communications and station lighting. Tents were used for billeting and also for support facilities. Time was the all-important factor and ALGs serve its purpose if available for only a few days. As the forward area became the rear area, an advanced landing field could be improved for medium bomber use, but initially they primarily served fighter and transport groups. Based on the experience obtained in the North African and Italian campaigns, fighter groups required an airfield 120 feet x 3600 feet long, and fighter-bomber groups required fields 120 feet x 5000 feet long. Medium bomb groups required 120 feet x 6000 feet runways. Runway types Instead of using rough, unimproved dirt strips, engineers used surfacing material necessary to strengthen the soil to support the weight of the aircraft and as a measure of insurance against the wet weather. Airfields were initially single runway landing strips which were laid down east–west (09/27) unless local conditions dictated a different runway direction. Sommerfeld Tracking ALGs laid in the UK were of Sommerfeld Tracking a form of stiffened steel wire mesh. Square-Mesh Track (SMT) The surfacing material selected for the building of advanced landing grounds during the first weeks after the Normandy invasion was known as square-mesh track (SMT). SMT, a British development, was material composed of heavy wire joined in three-inch squares. It was chosen over other surfacing materials because it was very lightweight, allowing sufficient quantities to be transported across the English channel on over-tasked landing craft. Easily workable, a SMT landing mat for fighters could be laid like a carpet in about one week. Prefabricated Hessian (PBS) After the initial batch of airfields was completed using SMT, the Army aviation engineers switched almost exclusively to another surfacing material known as prefabricated hessian (burlap) surfacing (PBS). Light and easily transportable, PBS did not create the dust problem encountered with SMT fields. Made of an asphalt-impregnated jute delivered in rolls 300 feet in length and 36 inches or 43 inches in width, PBS was laid in overlapping layers to produce a dust-free fair weather surface. It was also common to build airstrips using both SMT and PBS, laying SMT on top. Pierced Steel Plank (PSP) To provide an all season durable airfield for the RAF's 2TAF and the USAF Ninth Air Force's