78th Division was in reserve during the winter battles at Monte Cassino, but was then committed during Operation Diadem (the fourth and final Battle of Monte Cassino) on 15 May 1944. The division was ordered to press hard up the Liri Valley to outflank the defenders at Monastery Hill. Advancing along the crowded Highway 6 it reached Roccasecca railway station by 25 May and then moved into the rough country to the north, which was difficult for the supporting guns and vehicles. Once the Hitler Line was broken, 78th Division went into reserve on 3 June while armoured formations passed through for the pursuit to Lake Trasimeno. The division returned to the front on 10 June, advancing up the River Tiber against strengthening opposition before beginning an attack on the Trasimene Line on 21 June. After hard fighting the defences were breached on 28 June.