This was the Allied break-out of Major General Lucian K. Truscott’s US VI Corps of Lieutenant General Mark W. Clark’s US 5th Army from its 'Shingle' lodgement at Anzio (23/25 May 1944).
The lodgement of the VI Corps 1 was contained by General Alfred Schlemm’s I Fallschirmkorps and General Traugott Herr’s LXXVI Panzerkorps 2 within Generaloberst Eberhard von Mackensen’s 14th Army of Generalfeldmarschall Albert Kesselring’s Heeresgruppe 'C'.
The Allies and the Germans had realised by the beginning of 1944 that neither side could hope to achieve any decisive military result in Italy before the arrival of better weather in the spring, and had fallen largely onto the defensive alleviated by aggressive patrols and artillery duels as they embarked on the process of rebuilding the fighting capabilities blunted by the fighting on the Cassino and Anzio fronts.
In anticipation of the likely course of operations once the arrival of spring made these possible, Kesselring ordered the preparation of a new defence line behind the line of the 'Shingle' lodgement. This 'Cäsar-Linie' extended from Ostia at the mouth of the Tiber river just to the south of Rome through Albano, skirting south of the Alban hills to Valmontone and across Italy via Avezzano to the Adriatic coast at Pescara. Behind the western half of the 'Cäsar-Linie' was a subsidiary switch line which extended from the 'Cäsar-Linie' at a point in the Apennine mountains and extended westward past the north of Rome to reach the Tyrrhenian Sea near Civitavecchia. Kesselring planned that the 14th Army and, to its left, the 10th Army could pull back behind the 'Cäsar-Linie' if, or rather when, the need arose.
Meanwhile Truscott, promoted from command of the US 3rd Division to replace Major General John P. Lucas as commander of the VI Corps on 22 February, and his staff worked on the plans for a decisive attack as part of the general offensive which General the Hon. Sir Harold Alexander, commander-in-chief of the Allied Central Mediterranean Force, was planning for May and which would include the 'Diadem' major offensive on the 'Gustav-Linie' defences. The primary objective of the general offensive was to force the full engagement of Heeresgruppe 'C' and thereby remove any possibility of the redeployment of German formations from Italy to other theatres. It was also intended that the offensive should also trap as large a proportion of the 10th Army between the Allied forces advancing through and beyond the 'Gustav-Linie' and the VI Corps thrusting inland from Anzio.
During March, the Italian 2/82nd Waffengrenadierregiment 'Vendetta' and 29th Füsilierbataillon 'Debica' of SS-Obergruppenführer und General der Waffen-SS Karl Wolff’s 29th SS Waffengrenadierdivision (italienische Nr 1) arrived to reinforce the German units holding the Anzio perimeter. These two battalions were allocated to German formations, whose commanders later reported favourably on the capabilities of these Italian reinforcements, which were commanded by an ex-Blackshirt officer, Tenente Colonnello Carlo Federigo degli Oddi.
It was during March and May respectively that the US 34th Division and US 36th Division arrived at Anzio, and in the same period Major General G. W. R. Templer’s British 56th Division had been replaced by the British 5th Division. The time was approaching for the VI Corps to break out of the Anzio beach-head, and it was on 18 May that Alexander permitted the movement of the 36th Division into the beach-head. The advance of the II Corps along the coastal sector meant that the 36th Division, which was the 5th Army’s reserve division and not to be committed without Alexander’s authorisation, would not be needed on the main front, and could therefore be used to strengthen the break-out force. Its move into the beach-head would take four days, so the earliest that the break-out could take place would be 23 May, which coincided nicely with the fact that Lieutenant General Sir Oliver Leese’s 8th Army and Général de Corps d’Armée Alphonse Pierre Juin’s Corps Expéditionnaire Français (French Expeditionary Corps) would be attacking the 'Führer-Senger-Linie' defences on that day, and the II Corps advancing toward Terracina.
By a time late in May, the Anzio lodgement contained about 150,000 Allied troops in five US and two British divisions, and these faced five German divisions. The Germans occupied well-prepared defences, but were weak in officer and non-commissioned officer numbers and, by the time of the Allied offensive late in May, lacked reserves as they had been redeployed to the south to bolster the 10th Army in the 'Gustav-Linie' fighting.
But while there was no problem with the decision about the operational moment at which the break-out from Anzio was to be made, there were difficulties with the decision about the direction in which the break-out should be made. This resulted in disagreement between Alexander and Clark, and between their staffs.
In his thinking and consequent orders for the 'Diadem' offensive, Alexander had stressed that the primary aim was the destruction of German divisions, with the capture of Rome a secondary aim which would probably occur as a by-product of the primary aim. Clark discerned matters in exactly the opposite way, and saw Rome as the primary objective with the destruction of German formations as the secondary, but nonetheless very important, objective. Clark believed vehemently that the 5th Army’s trials and tribulations during the winter of 1943/44 deserved this prize.
So far as the break-out from the Anzio beach-head was concerned, therefore, Alexander felt that the VI Corps' operation, for which there were five US and two British divisions available, should be made along a north-easterly axis toward Valmontone in order to cut Highway 6 and thus sever the major line of retreat for Generaloberst Heinrich-Gottfried von Vietinghoff-Scheel’s 10th Army falling back from the Cassino front. Clark objected on the grounds first that this would require a dangerous flank march across the front of the German forces holding the dominating Alban Hills and second that when the II Corps reached Valmontone the 10th Army could easily escape the trap by withdrawing up the two good roads and many subsidiary tracks leading to the north-west from Highway 6 to Highway 5, the primary lateral road linking Rome and Pescara, and at one time the proposed axis for the advance of the advance of the British 8th Army, then commanded by General Sir Bernard Montgomery, on Rome. Clark believed that if the Germans reached this lateral, they would easily be able to deploy their formations into the 'Cäsar-Linie' defences. Alexander accepted Clark’s first point but disagreed with the second, and in general held that the fewer the lines of retreat available to the Germans, the greater would be the destruction visited on them by Allied air power.
Despite the fact that Alexander’s overall plan for 'Diadem' demanded that the VI Corps should strike inland and cut Highway 6 and thus sever the 10th Army's primary line of retreat, Clark asked Truscott to prepare alternatives and to ready his corps to switch from one to another at 48-hour notice. Of the four scenarios prepared by Truscott, 'Buffalo' called for an attack through Cisterna and into the gap in the hills, to cut Highway 6 at Valmontone. The 'Turtle' alternative was based on a main thrust to the left of the Alban hills to take Campoleone and Albano, and then press to the north for the capture of Rome. On 5 May Alexander selected 'Buffalo' and issued Clark with orders to this effect.
Clark was determined that the VI Corps should strike directly for Rome, however, and presented an argument to Alexander that the VI Corps lacked the strength to trap the 10th Army. Instead of emphasising his previous order, Alexander was conciliatory and gave the impression that a 'Turtle' push on Rome was still a possibility if 'Buffalo' experienced difficulties. On 6 May Clark informed Truscott that 'the capture of Rome is the only important objective and to be ready to execute Turtle as well as Buffalo'.
Even before Lieutenant General E. L. M. Burns’s Canadian I Corps of Leese’s British 8th Army broke through the left of their 'Führer-Senger-Linie' ('Hitler Line' to the Allies) defences to the north of Monte Cassino and the 'Gustav-Linie', so opening the way toward the Anzio lodgement and the 'Cäsar-Linie' defences just to the south of Rome, Kesselring and his subordinate commanders had become increasingly concerned by the penetration of the defences in the south, where Juin’s French Expeditionary Corps and Major General Geoffrey T. Keyes’s US II Corps, the latter attacking to the north-west from the line of the Garigliano river, had broken through to reach the highway linking Pico and Formio on 19 May.
Generalleutnant Smilo Freiherr von Lüttwitz’s 26th Panzerdivision was having some success in restabilising this part of the front’s central sector between Pico and Pontecorvo, but at the same time Generalleutnant Eberhard Rodt’s 15th Panzergrenadierdivision could not check the Allied advance nearer to the coast. With some hesitation, because of his uncertainty about the overall situation, Kesselring ordered the 14th Army to despatch Generalmajor Fritz Polack’s 29th Panzergrenadierdivision from Civitavecchia to block the II Corps' advance in the potentially strong defensive position along Highway 7 between Fondi and Terracina, where there was a final defile before Highway 7 debouched onto the flat land of the Pontine Marsh area, leading directly to the southern edge of the Allied beach-head at Anzio.
If the 29th Panzergrenadierdivision could stop the Americans here, Kesselring believed, there remained a chance to prevent the link-up of the two Allied forces. von Mackensen disagreed with this, believing instead that it would be better to hold back the 29th Panzergrenadierdivision for the defeat of the break-out he was sure was coming from the beach-head. When it received Kesselring’s order, therefore, the 14th Army's staff protested to Heeresgruppe 'C', and Kesselring found that his order had not been carried out only on his return from a visit to the front.
The two commanders' disagreement had a decidedly dire effect on the fate of the 29th Panzergrenadierdivision. If it had moved south at the time of Kesselring’s original order on 19 May, it would have had the time it needed to prepare its positions before the US formations reached the Terracina defile but, as it now happened, the division was forced to deploy straight off the march into battle without even adequate reconnaissance. It also found that it was too late to stop the US forces, which had already seized the high ground above the defile that would otherwise have become the basis of the Germans' defensive position. The 29th Panzergrenadierdivision nonetheless fought courageously and did indeed manage to hold Terracina until the night of 23/24 May before being compelled to fall back, together with the remnants of Generalleutnant Bernhard Steinmetz’s 94th Division and Generalleutnant Wilhelm Raapke’s 71st Division, through the Monti Lepini toward Highway 6 in order to avoid being cut off. On the Allied side of the line, matters were progressing along more amenable lines, and on 25 May the leading elements of the US II Corps established contact at Borgo Grappa with the US forces in the south-eastern part of the Anzio lodgement.
Meanwhile Truscott and his staff had been planning 'Buffalo' very carefully. The core of his plan was that the British 5th Division and US 1st Division on the left were to attack along the coast and up the Via Anziate to pin the 4th Fallschirmjägerdivision, 65th Division and 3rd Panzergrenadierdivision while the US 45th Division, US 1st Armored Division and US 3rd Division launched the main assault in the centre against the 362nd Division and 715th Division and advanced toward Campoleone, Velletri and Cisterna respectively. On the right, the 1st Special Service Force would protect the US assault’s right flank.
At 05.45 on 23 May 'Buffalo' began with a bombardment by 1,500 pieces of Allied artillery, which was followed after 40 minutes by a horde of attacks by Allied tactical warplanes, and then resumed as the infantry and armour moved forward. The fighting of 23 May was intense: the US 1st Armored Division lost 100 tanks and the US 3rd Division suffered 955 casualties, which was the greatest single-day figure for any US division during World War II. The Germans suffered too, with the 362nd Division reckoned to have lost 50% of its fighting strength.
The breakout started on 23 May with an attack on Cisterna by the US 3rd Division, US 1st Armored Division and 1st Special Service Force. It was then intended to pass the fresh US 36th Division with the 1st Armored Division through the breach in the German defences and on through the gap between the Alban Hills and the Monti Lepini toward Valmontone, giving the Alban Hills as wide a berth as possible. Major General William W. Eagles’s US 45th Division would protect the northern flank by widening the breach toward the Alban Hills, while two British formations, Loewen’s 1st Division and Gregson-Ellis’s 5th Division, held the northern perimeter against any relieving attack which Schlemm’s I Fallschirmkorps might choose to make, and also delivered a powerful feint out of the north-western edge of the lodgement. When they attacked, the US 1st Armored Division and US 3rd Division achieved total tactical surprise and opened a sizeable gap in the defences of Greiner’s 362nd Division and Hoffmann’s 715th Division. The latter broke first and tried to pull back toward the Monti Lepini, but the former stood its ground and, with the aid of airborne forces from the northern side of the beach-head, held the northern shoulder of the US breach.
von Mackensen had been convinced that the Allies would deliver their main thrust straight up the Via Anziate (Highway 7), and he was confident in that he had foreseen matters accurately once the ferocity of the British feint of 23/24 May was seen. Kesselring believed differently, however, and remained sure that the Allies intended to reach Highway 6 farther island. He therefore ordered Generalmajor Wilhelm Schmalz’s 1st Fallschirmpanzerdivision 'Hermann Göring', resting some 150 miles (240 km) away at Livorno, to move as rapidly as possible to Valmontone, where it was to hold Highway 6 open for the 10th Army, which was retreating to the north-west along this route from Cassino.
Kesselring had thus been compelled to commit his last reserve mobile division, a formation earmarked by the Oberkommando der Wehrmacht for redeployment to France to bolster the defences against 'Overlord', in order to check the US break-out. So acute had the German position round Anzio become that this Luftwaffe division had to run the major risk of moving to the south in daylight, and as a result suffered severe losses: during 25 May some of these German reinforcements were spotted moving south from Valmontone toward the location of the US break-out and were heavily bombed and strafed by Allied warplanes, and the VI Corps claimed that some 600 German vehicles had been destroyed and 400 more damaged. The figures will never be known with any accuracy, but as the US forces drove forward past Cisterna they found the roads blocked with burned-out German equipment.
Heavy fighting continued on 23, 24 and 25 May. During the afternoon of May 25 the US 3rd Division took Cisterna after a house-by-house battle to winkle out men of the 362nd Division, which had refused to withdraw and, as a consequence, had been effectively destroyed by the end of the day. By the end of 25 the US 3rd Division was moving into the Velletri gap near Cori, and at the same time elements of US 1st Armored Division were within 3 miles (4.8 km) of Valmontone and in contact with units of the 1st Fallschirmpanzerdivision 'Hermann Göring' which were just starting to arrive from Livorno.
By dusk on 25 May the US forces had secured a wide breach, Cisterna, Cori and the northern edge of the Monti Lepini were in US hands, and as noted above the leading elements of the II Corps, advancing north-west from Terracina, had made contact with a patrol from the beach-head. Thus the 5th Army was reunited after three and a half months of separation. The Germans had lost 2,500 prisoners by this time, but US losses had been by no means negligible: the 1st Armored Division had lost many tanks, and the 3rd Division had suffered more than 1,000 casualties on the first day alone, but both formations were nonetheless still full of fight.
Although the VI Corps had suffered more than 3,300 casualties in three days of fighting, 'Buffalo' was proceeding basically to plan, and Truscott was confident that a concerted attack by the US 1st Armored Division and US 3rd Division on the following day would place his men astride Highway 6.
Then, during the evening of 25 May, Truscott received a new order from Clark via his operations officer, Brigadier General Don W. Brann. This order was, in effect, to switch to 'Turtle' and thus turn the axis of his main attack through 90° from north-east to north-west. Although the attack toward Valmontone and Highway 6 was to be continued, the US 1st Armored Division was to be withdrawn and readied to exploit the planned breakthrough along the new axis, leaving the US 3rd Division to continue toward Valmontone with the 1st Special Service Force in support.
Clark informed Alexander of these developments late in the morning of 26 May, by which time the change was a fait accompli. Neither at the time nor later did Truscott approve of the change which, he felt, made it impossible to secure the more important objective of ensuring the destruction of the greater part of the 10th Army, but could not contact Clark to query the order and had therefore to comply.
Even as the VI Corps was starting its difficult change of axis on 26 May, Kesselring committed elements of four divisions into the Velletri gap in an effort to halt the US advance toward Highway 6 by the US 3rd Division, which was continuing its advance toward Valmontone and took Artena just 3 miles (4.8 km) south of Highway 6 near Valmontone, but was then checked by a quickly improvised grouping of the 1st Fallschirmpanzerdivision, Generalleutnant Hellmuth Böhlke’s 334th Division from the Adriatic sector, and Oberst Freiherr de la Salle’s 92nd Division recently activated near Rome. Thus the line of retreat was held open for seven divisions of the 10th Army, which lived to continue the fight for the rest of the Italian campaign.
There followed a four-day battle with the US 3rd Division before the Germans were compelled to fall back on 30 May.
The VI Corps made little progress on its new axis of attack until the US 1st Armored Division was in position on 29 May, when the front advanced to the 'Cäsar-Linie' defences. A swift breakthrough seemed unlikely until 30 May, when the US 36th Division found a gap in the 'Cäsar-Linie' defences at the junction of the I Fallschirmkorps and the LXXVI Panzerkorps. At this point the men of the US 3rd Division climbed the steep slopes of Monte Artemisio and thus threatened Velletri from the rear and obliged its German defenders to withdraw. This was the turning point of the battle, as the Germans fully appreciated, and when von Mackensen offered his resignation Kesselring accepted it and placed General Joachim Lemelsen in command of the 14th Army.
Increasing the pressure on the Germans still further, Clark allocated the US II Corps, which had fought its way to the north-west along the coast from the 'Gustav-Linie' in 'Diadem', to operate with the VI Corps on 25 May to attack around the eastern side of the Alban Hills and advance along Highway 6 to Rome.
On 2 June the 'Cäsar-Linie' defences broke under the mounting pressure, and the 14th Army began a fighting withdrawal through Rome. On the same day Adolf Hitler, still haunted by the nightmare of another urban battle akin to that which had seen the destruction of the 6th Army at Stalingrad, ordered Kesselring not to attempt to hold Rome.
During 3 June the German rearguards were steadily overwhelmed, and US forces entered Rome in the early hours of 4 June. Clark ensured that the credit for the seizure of Rome was wholly American by positioning military police at road junctions with orders to refuse entry to the city by British military personnel.
Although there is continuing controversy about the possible course of events had Lucas used his VI Corps more aggressively right from the start of 'Shingle', it is generally agreed that the initial Anzio plan was flawed inasmuch as the initial landing of two infantry divisions, with the support of special forces but without armour, clearly lacked the strength to achieve the objective of driving inland to sever Highway 6 and then holding off the inevitable German counterattacks as Kesselring redeployed his forces.
Even if it failed in its primary objective, 'Shingle' did secure major benefits for the Allied cause as, after the landings, the German high command abandoned plans to redeploy five of Kesselring’s best divisions to North-West Europe, with obvious benefits for the forthcoming 'Overlord'.
What is undeniable, however, is that as a result of Clark’s change of plan, 'Diadem' cost the US 5th Army and British 8th Army some 44,000 casualties but failed in its objective of destroying the 10th Army, and thereby condemned the Allies to another year of bloody battle, most especially around the 'Gotisch-Linie' between August 1944 and May 1945. Adding insult to this forthcoming injury is the probability that had the main effort of the VI Corps continued on the Valmontone axis on 26 May and the days following it, Clark could have reached Rome more quickly than he was able to do by the route to the north-west from Cisterna. The VI Corps also could have cut Highway 6 and put far greater pressure on the 10th Army than it did.