The fourth battle of Cassino or Operation Diadem (11-18 May 1944) was a large scale Allied attack that finally broke the stalemate on the Cassino front, and allowed the Allies to occupy Rome just before the start of Operation Overlord.
In the aftermath of the successful defence of the Salerno bridgehead, the Allies broke out, captured Naples, and attempted to push on to Rome. The Germans fought delaying actions at the Volturno Line (October 1943) and the Barbara Line (31 October-4 November 1943), and a more successful action on the Bernhardt Line (December 1943), which gave them time to build up their main defensive position, the Gustav Line. This ran up the Garigliano River, to the west of the Aurunci mountains, and then up the Rapido, which flowed out of the central Apennines. Along most of the line it ran through mountains, but there was one weak point - the valley of the Liri River, which flowed east down a fairly open valley, and ran into the Rapido to the south of Cassino, to form the Garigliano. The Liri valley thus became the main Allied objective over the next few months. The battle for the Bernhardt Line brought the Allies up to the Rapido and Garigliano, but the entrance to that valley was guarded by mountains on both flanks, most famously Monte Cassino to the north.
Over the next few months General Clark’s Fifth Army made a series of attacks on the Gustav Line, without achieving much success.
The first battle of Cassino (12 January-12 February 1944) had involved an Allied attack along most of the line, but very little went right. A French attack in the hills north of Cassino failed after a few days. The British attack across the Garigliano River had established a bridgehead over the river, but had failed to take the key higher ground. The American attack over the Rapido (battle of the Rapido, 20-22 January 1944) had ended in total disaster after only two days. A second attack, further up the Rapido, made some progress, but failed to take the monastery.
The second battle of Cassino (15-18 February 1944) was the most controversial of the four, as it began with the destruction by bombing of the ancient Benedictine Monastery on top of Monte Cassino. The bombing was followed by a series of infantry attacks carried out by the 4th Indian and 2nd New Zealand Divisions, but these weren’t coordinated with the bombing, and although they made some progress, once again the town and the monastery remained in German hands.
The third battle of Cassino (15-22 March 1944) was almost a repeat of the second, starting with a bombing raid, followed by attacked by the same two divisions. It also ended in failure.
By now Churchill was starting to get exasperated with the limited range of operations on the Italian front, and questioned Alexander, the Allied ground commander, about his overall strategy. By now Alexander was also ready for a new plan. The British Eighth Army was to be moved from the Adriatic front, where very little was happening, to join the US Fifth Army at Cassino. The Fifth Army had also received reinforcements. The new attack would take place along the twenty five miles from the coast to the Cassino area and would involve fourteen Allied divisions with a fifteenth in reserve.
On the left the US II Corps, made up of the newly arrived 85th and 88th Divisions, would attack across the Garigliano near the coast and attempt to advance along Highway 7 (the Appian Way). To their right the French Expeditionary Corps (General Juin), with two Moroccan, one Algerian and one French division, would cross the upper Garigliano and attack into the Aurunci Mountains. On their right the two divisions of the Canadian Corps would attack just to the north of the junction of the Rapido and Liri Rivers. Next was the British XIII Corps, with one Indian divison and three British divisions. This would cross the Rapido downstream of Cassino and attempt to break into the Liri valley. The 6th South African Armoured Division was posted in the rear of XIII as the reserve. Finally, on the right, the Polish II Corps, with two infantry divisions and an armoured brigade would attack Monte Cassino from the mountains to the north. The hope was that the German lines would crack. The seven divisions of Allied troops at Anzio and the troops at Cassino would meet up, and would trap and capture the bulk of the German troops before they could escape into northern Italy, where fresh defensive positions were being prepared. The large scale troop movements required for this plan were carried out in secret, mainly at night, and Kesselring, the German commander in Italy, didn’t learn about them until the attack began. The Allies also carried out deception measures, including practising amphibious operations around Naples.
Kesselring suspected that the Allies were planning to land somewhere to the north of Rome, so he kept his reserves in that area. He also began work on new defensive positions around Rome. The Hitler Line was built just a few miles to the north of the existing Gustav Line, and was meant to stop any Allied breakthrough on that front. The Caesar Line was built between Anzio and Rome, and was the last line of defence before Rome herself. These positions weren’t as strong as the Gustav Line, but they could have held the Allies up for some time.
The German troops on the Cassino front were split into two corps, forming the 10th Army. On their right the 14th Panzer Corps (Senger-Etterlin) was in command from the Liri to the coast, with the 94th Panzer Grenadier Division on the coastal sector (facing the US 2nd Corps) and the 71st Infantry Division facing the upper Garigliano and Juin’s French Expeditionary Corps. On the left was the 51st Mountain Corps (Feuerstein). Kampfgruppe Bode held the entrance to the Liri Valley (south of Cassino), facing the British 13th Corps. The 1st Paratroop Infantry Division held Cassino and Monte Cassino, facing part of 13th Corps and the Polish 2nd Corps (Anders). Finally came Kampfgruppe Ruffin in the mountains to the north-west of the monastery, facing the right wing of the Poles. When the attack began General Vietinghoff, commander of the 10th Army, and General Senger were both on leave in Germany and by the time they returned the battle was already lost.
Alexander’s plans came tantalisingly close to total success, and they did finally break the deadlock at Cassino. The attack began with a massive artillery bombardment, carried out by 1,600 guns along the entire front. This began at 11pm on 11 May, and briefly stunned the Germans. However they quickly recovered, and managed to hold their ground along most of the line. The Poles suffered heavy losses on Monastery Hill. The British and Canadians established a small bridgehead across the Rapido, but were unable to move into the Liri valley. On the coast the fresh US troops made a short advance before being stopped.
However the Germans had one weak spot in their lines - the Aurunci Mountains. Kesselring believed that the rugged terrain here would make any large scale advance impossible, and so it was only thinly defended. He had also lost track of Juin’s French troops, which included a large number of men who lived in equally or more rugged terrain in North Africa. They were able to break through the German lines, and within a few days had advanced across the mountains and had reached a position in the Liri valley several miles to the west of Cassino. The 2nd Moroccan Infantry Division made the initial breakthrough, and the Corps then spread out across the mountains, supported by thousands of pack mules. On 17 May the 3rd Algerian Infantry Division (supported by Sherman tanks from the US 1st Armored Division) then captured the mountain town of Esperia, ten miles to the south-west of Cassino and a key point in the Hitler Line. Not only had they outflanked the Gustav Line, they had also begun the penetration of the next German defensive line. The Algerians suffered heavy casualties in an ambush as they advanced north into the Liri valley, but soon cleared the Germans off the key Monte d’Oro, north-west of the town, and were able to advance into the valley beyond.
The French advance also encouraged the British and Americans. The Eighth Army was able to expand its bridgehead across the Rapido, and by 17 May, six days into the offensive, they and the French were about to cut off the defenders of Cassino. The British right wing reached Piumarola, three and a half miles to the west/ south west of Cassino. Kesselring was finally forced to order the troops in Cassino town and on Monastery Hill to retreat. He had to issue a personal order to the 1st Parachute Division, in the Monastery ruins, but on the night of 17-18 May they finally retreated. On 18 May the Poles were able to raise their flag above the Monastery ruins.
The Allies finally had a chance to win a decisive victory in Italy. Kesselring’s army was still intact, and making a fighting retreat up the Liri Valley, but they only had a narrow escape route. By 18 May the Germans had retreated into the Adolf Hitler Line (also known as the Dora Line), but they were aware that this could only be held if the troops at Anzio, in its rear, were contained. In the meantime the Americans and French on the Fifth Army continued their advance. On 19 May the Americans reached Gaeta. On 20 May the French advanced towards Pico, and on 21 May the Americans leapfrogged 11 miles up the coast to Sperlonga. On 22 May Kesselring finally ordered a retreat from the Liri Valley via Valmontone. On the same day the Americans on the coast captured Terracina, the last defensive position between them and Anzio.
Part of Alexander’s plan was for the troops at Anzio to attack north and capture the town of Valmontone, on Highway 6, thus cutting Kesselring’s best line of retreat. Unfortunately General Clark didn’t agree with that plan. On military grounds he didn’t believe that this move would actually trap the Germans, as they would be able to use other routes further inland. He also worried that this advance would leave his troops exposed to a counterattack from the German troops in the Alban Hills. Perhaps more importantly, at least to Clark, was the prize of Rome. He was determined to make sure that it would be his troops who captured the Eternal City and not the British Eighth Army.
The Allied attack began on 22 May with diversionary attacks by the British at Anzio and a successful attack on the Adolf Hitler Line by the Canadians. On 23 May the troops at Anzio went onto the offensive. At 5.30am the 500 guns within the beachhead opened fire. A bombing raid then hit Cisterna, before four divisions attacked towards the town. The Germans held out until 25 May, when the 362nd Division was finally forced out of the town. On the Adolf Hitler Line the British broke the line on 24 May, but the Germans then counterattacked, slowing the advance.
Early on 25 May advancing troops from the US II Corps finally joined up with the troops at Anzio, ended the isolation of the beachhead. On the same day the Canadians crossed the Melfa River in the Lira valley, British troops took Monte Cairo and the Poles reached Piedimonte.
Cisterna also fell on 25 May. General Truscott, commander of VI Corps, began the advance towards Valmontone, but much to his anger Clark intervened, and ordered him to turn to the north-west to advance towards Rome. In order to make it look as if he was at least partly obeying his orders, Clark allowed one third of the corps to continue towards Valmontone, but this wasn’t enough to stop the Germans, and the endangered right wing of Kesselring’s army from Cassino was able to escape intact. The majority of Allied commanders in Italy, British and American, were outraged at Clark’s actions, which formed one of the few blots on his otherwise impressive record.
Clark’s gamble might have ended in disaster, as he still had to break through the Caesar Line in the Alban Hills if he was to reach Rome. If he had been held up at this position, and the troops he had allowed to escape from the Cassino position had been given the time to recover and help man the new lines, then the Allies might have been trapped south of Rome once again. This came close to happening. On 26 May Truscott turned north, but hit the strongest point in the Caesar Line, around Albano. To the east the Germans were able to escape from the Liri and man the Caesar Line around Valmontone. Once again a chance to win a major strategic victory in Italy had slipped away. To make things worse, Truscott’s limited move east had occupied Highway 6, slowing down the Eighth Army advance up the Liri Valley.
Luckily for Clark, the Germans hadn’t quite had enough time to get fully organised, and there was a weak spot in their line at Monte Artemisio, just to the north of the town of Velletri. This area fell on the boundary between two German units, and neither had properly manned it. Orders to do so had been issued, but not obeyed in time. On the night of 30 May 8,000 Americans from the 36th Division managed to sneak through the gap and take up a position on higher ground begin the Caesar Line. This ended any chance the Germans had of defending Rome. On 2 June Kesselring asked for permission to abandon Rome, and it was granted on 3 June. He then declared her to be an open city. General Clark was able to make his triumphant entry into the city on 4 June 1944, and gained two days of good publicity before the D-Day landings on 6 June wiped Italy from the headlines.
The fourth battle of Cassino was a costly victory. The Allies lost 40,000 dead, wounded and missing, the Germans 38,000. Rome had fallen, but the survivors from the German 10th Army had been able to escape north. Over the next few months the Allies pushed north. The Germans attempted to defend the Trasimene Line, the Arezzo Line and the Arno Line, but they were only finally able to stop the Allied advance at the Gothic Line in the northern Apennines. After a two month long advance, the Allies were finally stopped just short of the Po Valley, and the Italian campaign dragged on into 1945.