United Kingdom Invasion of Italy Winter Line Gothic Line 1945 Spring Offensive Operation Diadem, also referred 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 U.S. VI Corps, moving northeast from Anzio, was at the point of cutting off the German line of retreat when Lieutenant General Mark W. Clark, commander of the Fifth Army, inexplicably ordered them to turn northwest and advance on Rome instead.

In his autobiography, General Mark W. Clark describes how the French Expeditionary Corps (FEC) broke through the Gustav Line in May 1944.

The French surprised the enemy and quickly seized key terrain including Mounts Faito Cerasola and high ground near Castelforte.

D'Oro, Ausonia and Esperia were seized in one of the most brilliant and daring advances of the war in Italy, and by May 16 the French Expeditionary Corps had thrust forward some ten miles on their left flank to Mount Revole, with the remainder of their front slanting back somewhat to keep contact with the British 8th Army.

The 8th Army's delay made Juin's task more difficult because he was moving forward so rapidly that his right flank---adjacent to the British---constantly was exposed to counter-attacks.

[1] In a letter to future Marshal Juin, General Mark Clark paid tribute to the Tirailleur units and Goumiers of the CEF in particular:For me, it has been a deep source of satisfaction to see how the vital part played by the French troops of the Fifth Army throughout our Italian campaign against the common enemy has been universally acknowledged.

Nevertheless, not satisfied with this, you and all your people have added a new epic chapter to the history of France; you have gladdened the hearts of your compatriots, giving them comfort and hope as they languish under the heavy and humiliating yoke of a hated invader.