The battle of the Trasimeno Line (20 June-2 July 1944) saw the Allies break through the first significant defensive line that the Germans had been able to create in the aftermath of the fourth battle of Cassino and the fall of Rome (Italian Campaign).
The long deadlock on the Cassino front had finally been broken by Operation Diadem, a joint Fifth and Eighth Army attack (Fourth battle of Cassino), followed by the breakout from the Anzio beachhead. On 4 June the Allies finally captured Rome, their main target since the autumn of 1943, but a chance to destroy the German armies south of Rome had been missed.
Attention now turned to the pursuit of the retreating Germans. The two German armies weren’t yet level with each other. The badly damaged 14th Army, on the coast, was further north than the stronger 10th Army, retreating from Cassino. Alexander’s plan was to use the Eighth Army to pin down the 10th Army, and the Fifth Army to pursue and defeat the 14th Army. However General Clark, commander of the Fifth Army, had problems of his own. The most serious was that a series of his best units were about to be withdrawn to take part in Operation Dragoon, the invasion of the south of France. His supply lines still ran down to Naples, in particular for fuel as that was still the nearest port to the front that could take tankers. One of his first targets was thus Civitavecchia, forty miles to the north-west of Rome.
On the German side Kesselring was aware of the weakness of the 14th Army, and of the danger that posed to the right flank of the 10th Army. To make things worse the Germans had destroyed every bridge over the Tiber between Rome and Orvieto, sixty miles to the north, making it difficult to get reinforcements to the 14th Army. Kesselring’s aim was to delay the Allied advance for as long as possible, to give his engineers time to work on the Gothic Line, a defensive position in the northern Apennines. Kesselring’s immediate response was to move all reinforcements west of the Tiber to support the 14th Army, while further north a series of potential defensive lines were chosen.
The first of these was the Dora Line, which ran from Orbetello on the coast seventy miles to the north-west of Rome, east to Lake Bolsena and then to Narni, forty miles north of Rome. From there it ran south-east for twenty miles to Rieti, and then east for thirty miles to L’Azuila, before entering the Gran Sasso d’Italia and crossing the Apennines to reach the Adriatic. Just to the north-east of the lake was Orvieto, and the first bridge over the Tiber that hadn’t been destroyed (mainly by the Germans themselves). This line didn’t last for long. To the east of Lake Bolsena the South African 6th Armoured Division broke through the line, and on 10-11 June threatened Orvieto and the key bridge. The Germans held on for a few days, but had to retreat on 14 June. The Allied advance continued on both flanks, but stopped at the second German defensive line.
This was the Frieda Line, also often called the Trasimeno Line, or the Albert Line. This began near Piombino, thirty miles to the north-west of Grosseto. It then ran north-east for thirty-five miles to Radicondoli, and from there to Lake Trasimeno. From the lake it ran east to Perugia and then on to Foligno before crossing the Apennines to reach the Adriatic near Porto Civitanova.
The western part of the line was held by the 14th Army. The 1st Parachute Corps (356th Infantry, 4th Parachute, 26th Panzer and 29th Panzer Grenadier Divisions) was on the left, the 14th Panzer Corps (90th Panzer Grenadier, 20th Luftwaffe, 3rd Panzer Grenadier and 162nd Turkestan Divisions) was in the centre and the 75th Corps (19th Anti-Aircraft Division) was on the coast.
The centre of the line, around Lake Trasimeno, was held by the 76th Panzer Corps, 10th Army. This included the 1st Parachute, 334th Infantry and Hermann Goering Armoured Divisions.
The main Allied attacks came to the south-west of the lake. On the right the 13th Corps, Eighth Army, attacked around Chiusi. In the centre the French Expeditionary Force was to attack towards Siena. On the left the US Fifth Army was to attack up the coast, aiming at Piombino and then Cecina.
The British attack began on 20 June. The 78th Division attacked east of Chiusi and the South African 6th Armoured to the west. The British 4th Division and Canadian 1st Armoured Brigade were in reserve. They came up against the 76th Panzer Corps, which held out for over a week, before the line was finally broken on 28 June. The British reached Foiano, 17 miles to the north of Chiusi, and north-west of the lake, on 2 July, forcing the Germans to abandon the Trasmino Line and withdraw north towards the Arezzo Line, the next defensive position.
Elsewhere the Germans had also come under pressure. In the centre the French attacked on 21 June, hitting the 4th Parachute and 356th Infantry Divisions. The attack was carried out by the 2nd Moroccan and 3rd Algerian Divisions. The Algerians captured Siena on 3 July, and were then removed to take part in Operation Dragoon. They were replaced by the 4th Moroccan Division, which by 7 July had almost reached Poggibonso, 14 miles further to the north-west.
On the left the US 36th Division advanced up the coast, taking Follonica on 23 June and Pimobino on 26 June. The division was then withdrawn and sent to Naples ready to take part in Operation Dragoon. It was replaced by the 34th Division, which attacked on the day it reached the front, and had completed the capture of Cecina by 2 July. On their right the 1st Armoured Division attacked towards Volterra (east of Cecina), but were replaced by the 88th Division before the town fell on 8 July, bringing the two parts of the US advance into line with each other.