text: Support to Large-Scale Ground Combat
  Bloody River
  The Allied Landings in Italy in September 1943 were followed quickly by the liberation
  of Naples. The crossing of the Volturno River in October had tied down German forces
  in southern Italy, and the next river crossing (into the Liri Valley) was needed to draw
  German troops south to ensure success of the Anzio Landing on Italy’s west coast. In
  theory, the enemy would be caught in a great pincer movement (now called a double
  envelopment).
  By year’s end, a reinforced German army of 23 divisions consisting of 215,000 troops
  engaged in the south as 265,000 troops in reserve in the north were conducting a slow
  withdrawal under pressure from the United States Fifth Army, the Commonwealth, and
  the Allied forces of the British Eighth Army. South of Rome, the Germans constructed
  three major defensive lines: the Barbara Line, the Bernhard (or Reinhard) Line, and
  the most formidable of the three belts—the Gustav Line. The Gustav Line was a system
  of sophisticated interlocking defenses, anchored on Monte Cassino, that stretched
  across the rugged, narrowest point of the peninsula along the Garigliano and Rapido
  Rivers.
  The Rapido River was incorporated into the Gustav Line and formed a natural moat,
  protecting Monte Cassino. Rapido is an Italian word that means fast or rapid, and the
  river was appropriately named. The banks of the Rapido were very steep and, in some
  places, vertical. The shallow crossing areas of the Rapido had been scouted by the
  Germans, allowing for concentrated, accurate artillery fire. Artillery fire originated from
  well concealed gun pits that had been blasted out of the solid rock in the mountainside.
  Before the Allied soldiers could get close to the river and attempt the crossing, they
  had to contend with flooded ground along the river banks. The Germans had diverted
  the Rapido by damming the river near crossing points. Allied soldiers were forced to
  walk and crawl across the submerged, near-freezing ground to reach the river, carrying
  all of their heavy equipment across the flooded fields. The soggy terrain had made it
  impossible to use heavy, tracked vehicles. Tanks could only move single-file on steel
  matting laid down by engineering companies. The Germans had only to knock out the
  lead tank to render the remaining tanks helpless.
  After they crossed the river, the Allied soldiers encountered entanglements of barbed
  wire and extensive minefields. While clearing paths across the minefields, the soldiers
  were exposed to interlocking machine gun fire from concrete pillboxes. The Germans
  cleared the river banks of all obstructions to provide clear fields of fire. After Allied
  tanks crossed the river, they then had to contend with antitank ditches. As Allied troops
  finally began their attack uphill, the rocky hillsides proved to be a natural, well
  protected, concealed fighting position for the Germans. The man-made obstacles of
  the Gustav Line added to the natural Italian terrain features, making Monte Cassino a
  defender’s dream and an attacking army’s nightmare.
  ATP 3-90.4 describes the following primary mobility tasks:
  * Conduct breaching.
  * Conduct route and area clearance.
  * Conduct a gap crossing.
  * Construct and maintain combat roads and trails.
  * Construct and maintain forward airfields and landing zones.
  * Conduct traffic management and enforcement.