The 'Battle of the Trasimene-Linie' was fought between Allied and German forces to the south and north of the 'Trasimene-Linie', a German defensive line extending to each side of Lake Trasimene in north central Italy (10 June/23 July 1944).
The line, sometimes called the 'Albert-Linie', was constructed on the instructions of Generalfeldmarschall Albert Kesselring, the Oberbefehlshaber 'Süd-West', to delay the Allied northward advance in Italy, to the west of the Apennine mountain range, in the middle of June 1944 and thereby buy time for the German forces to withdraw troops to the 'Gotische-Linie' and finalise the preparation of its defences.
After the US occupation of Rome, the Italian capital, on 4 June 1944 following the successful breakthrough at Monte Cassino and Anzio during 'Diadem' in May 1944, the 14th Army and [10th Army fell back to the north, the former along the Tyrrhenian Sea coast and the latter through central Italy and the Adriatic Sea coast. The 10th Army escaped because Lieutenant General Mark W. Clark ordered Major General Lucian K. Truscott to choose 'Turtle' for an advance toward Rome rather than 'Buffalo' as ordered by General the Hon. Sir Harold Alexander, which would have cut Highway 6 at Valmonte. There was a huge gap between the armies and with the Allies advancing some 6 miles (10 km) per day, the flanks of both German armies were exposed and encirclement was threatened.
Two days after the US 5th Army’s occupation of Rome on 4 June, Alexander, commander of the Allied Armies in Italy, received orders from his superior, General Sir Henry Maitland Wilson, the Allied Supreme Commander in the Mediterranean Theatre of Operations, to push the retreating forces 170 miles (270 km) north to a line extending between Pisa and Rimini (i.e. the 'Gotisch-Line') as quickly as possible to prevent the Germans from creating any any sort of coherent defence in central Italy.
On Clark’s US 5th Army front, Truscott’s US VI Corps drove up the coast along Highway 1 and Major General G. Keyes’s US II Corps along Highway 2 towards Viterbo. To their right the Lieutenant General S. C. Kirkman’s British XIII Corps, which was an element of Lieutenant General Sir Oliver Leese’s British 8th Army, advanced up Highway 3 toward Terni and Perugia while Lieutenant General C. W. Allfrey’s British V Corps advanced up the Adriatic coast.
Between 4 June and 16 June, and while his forces maintained contact with the advancing Allies, Kesselring executed a remarkable and unorthodox manoeuvre with his depleted divisions, resulting in his two armies coming intro alignment and uniting their wings on the defensive positions on the 'Trasimene-Linie'. Remarkable though this was, Kesselring was probably helped by the confusion caused in the Allied advance by the relief of the US II and VI Corps by Major General Willis D. Crittenberger’s US IV Corps and Général de Corps d’Armée Alphonse Pierre Juin’s Corps Expéditionnaire Français. Lieutenant General R. L. McCreery’s British X Corps, had also been brought into the line on the XIII Corps' right, while the V Corps had been relieved by Generał dywizji Władysław Anders’s Polish II Corps.
By the last week of June the Allies were facing the German defences of the 'Trasimene-Linie'. General Joachim Lemelsen’s 14th Army had General Fridolin von Senger und Etterlin’s XIV Panzerkorps facing the US IV Corps on the western coast and General Alfred Schlemm’s I Fallschirmkorps facing the Corps Expéditionnaire Français beside them. On 22 June, a US armoured attack near Massa Marittima was defeated by a German tank platoon of the 504th schwere Panzerabteilung, whose PzKpfW VI Tiger I heavy tanks knocked out 11 Sherman medium tanks, while the terrified US tank crews abandoned another 12. The Germans suffered no losses. Four other Sherman tanks were knocked out by two Tiger tanks of the 508th schwere Panzerabteilung on 12 July near Collesalvetti.
Generaloberst Heinrich von Vietinghoff-Scheel’s 10th Army had General Traugott Herr’s LXXVI Panzerkorps facing the XIII and X Corps, and General Valentin Feurstein’s LI Gebirgskorps facing the Polish II Corps on the Adriatic end of the front. The strongest German defences were around the lake itself, where Major General C. F. Keightley’s British 78th Division of the the XIII Corps was involved in severe fighting on 17 June at Città della Pieve and 21 June at San Fatucchio. By 24 June the British forces had worked their way round to the northern shore and linked with Major General A. D. Ward’s British 4th Division and Major General D. W. Reid’s Indian 10th Division of the X Corps as the German defenders withdrew toward Arezzo. On 8 July, the 2nd Kompanie of the 508th schwere Panzerabteilung knocked out four British Sherman tanks near Tavarnelle Val di Pesa to the south-west of Florence.
The US IV Corps also found progress slow but by 1 July had crossed the Cecina river and was within 20 miles (32 km) of Livorno. Meanwhile, the Corps Expéditionnaire Français had been checked on the Orcia river to the west of Lake Trasimene until the German airborne forces pulled back on 27 June, allowing the French to enter Siena on 3 July.