Fascist Italy invaded Greece on 28 October 1940 and a general mobilization was declared. The 1st Regiment quickly reached its full strength, and on 1 November sailed from Elefsina to Volos, to be used as a reserve for the Greek army fighting in Epirus. The regiment arrived at Volos on 4 November. Soon after it was bombarded by the Italian Royal Air Force. Over the next two months it followed the advance of the Greek army, moving on foot via Trikala and Florina. The regiment was finally sent to the front line in early January, when it took over a front sector in Mount Tomorr, under the command of 16th Infantry Brigade (soon expanded into the 16th Infantry Division). The regiment fought its most important battle of the war during the Italian Spring Offensive in March 1941, at the battle of Teke Hill. Following the German invasion of Greece on 6 April, and the rapid advance of the German forces, the Greek army in Albania started to retreat. The regiment retreated via Moscopole, Erseka, Konitsa, and Zagori, reaching Metsovo, where it was ordered disbanded after the capitulation of the Greek army in Epirus to the Germans (21 April).