Progress for the Allied Armies in Italy (AAI), commanded by General Sir Harold Alexander, towards the end of 1943 had slowed down considerably, due mainly to a combination of worsening weather, stiffening German resistance and the Winter Line (also known as the Gustav Line, a series of formidable defences the Germans had created). The Eighth Army, operating on the Adriatic coast, had already pierced the Gustav Line at its eastern end. However, the appalling weather conditions forbade further progress and so operations there were closed down. As a result, the relatively intact 5th Division was available elsewhere. Therefore, in early January 1944 the division was transferred from the Eighth Army, now under Lieutenant-General Sir Oliver Leese, to the western side of Italy to join Lieutenant-General Richard McCreery's British X Corps. X Corps, stationed along the Garigliano river, was part of Lieutenant General Mark W. Clark's U.S. Fifth Army at the time. The division, now commanded by Major-General Philip Gregson-Ellis and with the veteran 201st Guards Brigade under command, crossed the Garigliano river as part of the First Battle of Monte Cassino.