The Battle of San Pietro Infine (commonly referred to as the "Battle of San Pietro") was a major engagement from 8–17 December 1943, in the Italian Campaign of World War II involving Allied forces attacking from the south against heavily fortified positions of the German "Winter Line" in and around the town of San Pietro Infine, just south of Monte Cassino about halfway between Naples and Rome.
The eventual Allied victory in the battle was crucial in the ultimate drive to the north to liberate Rome. The battle is also remembered as the first in which the troops of the Royal Italian Army (Regio Esercito) fought as co-belligerents of the Allies following the armistice with Italy. The original town of San Pietro Infine was destroyed in the battle; the modern, rebuilt town of the same name is located a few hundred meters away.
Background
North Africa and Sicily
The Allied invasion of Italy from the south followed the Allied successes in North Africa. Lieutenant General Bernard Montgomery's British Eighth Army advanced from the east following the Second Battle of El Alamein and the British-American invasion of French North Africa by Lieutenant General Kenneth Anderson's British First Army in Operation Torch had led to the surrender of almost 250,000 Axis forces in North Africa in May 1943.
The Germans retreated to the island of Sicily and on the night of 9/10 July 1943, an Allied armada of 2,590 vessels launched one of the largest combined operations of World War II: the Allied invasion of Sicily (Operation Husky). The invasion was launched by the American Seventh Army, under Lieutenant General George S. Patton Jr., and the British Eighth Army, under Lieutenant General Sir Bernard Montgomery. Both armies were under the command of the 15th Army Group, commanded by General Sir Harold Alexander. Over the next five weeks, 500,000 Allied soldiers, sailors, and airmen fought German and Italian forces for control of the island. Although the Allied powers were victorious, the Axis managed to evacuate over 100,000 men and 10,000 vehicles from Sicily across the Straits of Messina during the first seventeen days in August. The Allies then invaded the Italian mainland in early September 1943 at Salerno (Operation Avalanche), in Calabria (Operation Baytown) and Taranto (Operation Slapstick).
On 8 September, before the main invasion at Salerno by American Lieutenant General Mark W. Clark's Fifth Army (which contained significant British units), the surrender of Italy to the Allies was announced. Italian units ceased combat, and the Royal Italian Navy sailed to Allied ports to surrender. This changed the German defensive strategy greatly, and the Germans now regarded their former allies as enemies and moved to disarm Italian units and occupy important defensive positions. The invasion at Salerno was ultimately successful, although the Allies sustained heavy casualties, and subsequently captured nearby Naples on 1 October. German forces then withdrew to the north, towards Rome, and dug in along a series of well-fortified lines. By late 1943 the fighting had reached the Winter Line (also known as the Gustav Line).
Italy
The German Commander-in-Chief (C-in-C) Albert Kesselring—had marked out the Winter Line as three parallel defensive systems to the south of Rome. The defensives lines were called the Reinhard Line, Gustav Line and Hitler Line, placed one from the other, taking advantage of the point at which the Italian Peninsula is narrowest; they served as a formidable series of obstacles in the path of the Allied march toward Rome. The Reinhard was the southernmost of the three and was the German fall-back position from the Barbara Line and Volturno Line further to the south as German forces retreated gradually up the peninsula. (The Reinhard was also called the Bernhardt Line.) The Reinhard was actually a southern bulge in the stronger Gustav line to the north. On the eastern side, the Reinhard went from the Sangro River to the Adriatic Sea (along which length it was identical to the Gustav Line); then, in the west, it bulged south from Cassino to incorporate the mountains overlooking the approaches to the Liri Valley and then moved west to the mouth of the Garigliano River. The line passed directly through the town of San Pietro Infine, blocking the Mignano Gap, the pass through which Route 6, the main road up the center of Italy from Naples to Rome, ran toward Cassino and the entrance to the Liri valley.