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 .

`` Diadem '' was supported Supporting by air attacks Attack called Operation Strangle .

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 .

General Sir Harold Alexander , Commander-in-Chief of the Allied Armies in Italy , planned Arranging `` Diadem '' to coordinate roughly with the invasion of Normandy , so that German forces Military_operation would be tied Connect down in Italy , and could not be redeployed to France .

`` Diadem '' was launched Motion at 23:00 pm on 11 May 1944 by elements of the British 4th Infantry Division and 8th Indian Infantry Division , with supporting Supporting fire from the 1st Canadian Armoured Brigade .