Operation Military_operation Diadem , also referred Name_conferral to as the Fourth Battle of Monte Cassino or , in Canada , the Battle of the Liri Valley , was an offensive operation undertaken by the Allies of World War II ( U.S. Fifth Army and British Eighth Army ) in May 1944 , as part of the Italian Campaign of World War II .

The object of `` Diadem '' was to break Bodily_harm the German defenses on the Gustav Line ( the western half of the Winter Line ) and open Openness up the Liri Valley , the main route to Rome .

This broke Destroying into the heart of the German defenses Defending in the Liri valley against strong opposition and drew Motion in German theater reserves , reducing Cause_change_of_position_on_a_scale pressure on the Anzio beachhead .

There is much speculation that he did this so that his Fifth Army would capture Conquering Rome ahead of the Eighth Army advancing up the Liri Valley .