The battle of the Arno Line (23 July -31 August 1944) saw the Germans delay the Allied advance on the Arno west of Florence for over a month, allowing more work to be carried out on the Gothic Line, further into the mountains. When the Allies did attack it was as part of a wider assault on the Gothic Line, and the Arno line fell without much serious fighting.
In the aftermath of the Fourth battle of Cassino, and the fall of Rome on 4 June, the Germans began to fall back towards the northern Apennines, where they had originally planned to make a stand before the Allied invasion of Rome. Kesselring was constructing a major defensive position in the mountains, the Gothic Line, and wanted to win time further south to allow the work to be completed. As a result the Germans attempted to hold a series of defensive lines further to the south. The first of these, the Dora Line, fell without much of a fight, but the second, the Frieda or Trasimeno Line, held out from 20 June-2 July 1944. Kesselring then decided to use the next two lines for delaying actions only, to avoid losing too many troops south of the mountains. The first of these, the Arezzo Line, defended the ports of Livorno and Ancona, and the communications centre of Arezzo. The Allies came up to the line at the end of the first week of July, and broke through it in the centre on 15-16 July. Ancona fell to the Poles on 17-18 July, and all along the front the Allies pushed on towards the Arno Line.
This line began at the mouth of the Arno, ran east through Pisa and Florence and then crossed the Apennines to reach the Adriatic along the northern bank of the Metauro. The defenders of the line did have one unusual problem - Kesselring didn’t want to risk damaging the artistic treasures of Florence, and so ordered his troops not to fight in the city. They did destroy all the bridges apart from the Ponte Vecchio bridge, including a number of other medieval bridges, but Florence was thus always a weak point in the line.
The Allied advance soon brought them up to the Arno. In the west the US 34th Division reached the mouth of the Arno and the southern part of Pisa on 23 July. The 91st Division reached the river north of Pontedera on 24-25 July, and the 88th Division reached it a little further to the east.
On the right the 8th Indian and 2nd New Zealand Divisions from the Eighth Army reached the Arno between Florence and Empoli on 3 August, and on the same day the leading troops from the South African 6th Armoured Division entered the southern suburbs of Florence.
In the centre the French Expeditionary Corps was withdrawn from the advance while still ten miles short of the Arno, and moved to Naples to take part in Operation Dragoon. The Eighth Army took over this part of the front.
Alexander’s first plan was to attack the centre of the Arno Line and then the Gothic Line, using the Fifth and Eighth Armies to attack in the mountains north of Florence, but this required the expert mountain troops of the French Expeditionary Force. This was then removed from his army to take part in the invasion of the south of France, forcing Alexander to change his plans after General Leese, commander of the Eighth Army, objected.
The new plan was for the Eighth Army to move back to the Adriatic coast and attack towards Rimini. The Germans would be forced to move their reserves east to deal with the new threat, allowing the Fifth Army to attempt to punch north across the Apennines towards Bologna and the Po valley. The British 13th Corps would remain in the centre, and come under the control of Clark’s Fifth Army. The attack on the Arno Line was seen as part of a wider assault on the Gothic Line, Operation Olive.
Unfortunately for the Allies Kesselring had already decided that this was the most likely Allied plan, and had moved reinforcements east.
Before moving east the Eighth Army did capture Florence in early August. Kesselring didn’t want to fight in the city and risk damage to its artistic treasures. On 2 August he decided to abandon the city, and by 4 August the Germans had pulled back four miles to the Heinrich Mountain Line, in the Mugello Hills. The last German troops left the city on 7 August, and the Allies quickly occupied it.
The Fifth Army remained static into mid-August while Clark reorganised his forces. The 1st Armored Division was finally able to adopt a new organisational setup that had been developed in response to its own combat experience. Other divisions were withdrawn from the front to get a much needed rest. The 4th Corps (Crittenberger) was posted on the left, covering 23 miles from the coast to the village of Capanne. Task Force 45, made up of various units converted into infantry, held the left of the corps front and the 1st Armored Division held the right. On the US right the 2nd Corps (Keyes) moved to the front, taking over control of the 85th 88th and 91st Divisions. The 91st held the front, which ran for seven miles from Capanne to the British 13th Corps, leaving the other two out of the line. This allowed four infantry and one armoured divisions to rest and prepare for the assault on the Gothic Line. Clark intended to make his main effort on his right, where his 2nd Corps would advance north from Florence, with the British 13th Corps on its right.
On the German side the Arno was defended by the Fourteenth Army (Lemelsen). The German left, from Florence to Empoli, was defended by the 1st Parachute Corps (Schlemm) which contained the 4th Parachute, 356th and 362nd Infantry Divisions. On the German right was the 14th Panzer Corps (von Senger), with the 65th Infantry and 16th SS Panzer Grenadier Divisions.
The Eighth Army offensive got under way on 25 August. The Germans only had light forces defending the eastern end of the Arno Line, and it quickly fell. The Eighth Army broke through both the Arno and Gothic Line positions in the east, and took 4,000 prisoners, before the autumn rains began, and the offensive slowed down several miles south of Rimini. Battles at Gemmano and Rimini saw the British make progress, but the advance ended in the Romagna, where the Eighth Army got bogged down the ‘battle of the Rivers’ which lasted into December before the Eighth Army stopped for the winter.
In the centre General Clark was able to take advantage of the German troop movements. On 29 August Kesselring ordered General Lemelsen to withdraw from the Arno, and the retreat began on 31 August. The Fifth Army was thus able to make an almost unopposed crossing of the Arno. The northern part of Pisa fell on 2 September. By 5 September 4th Corps had captured Lucca, Monte Pisano and Monte Albano, and the advance then came to a halt as German resistance hardened. On the right 13th Corps also reached a line 5-10 miles north of the Arno. In the centre the US 2nd Corps also followed the German retreat. The focus of Allied attention then moved to the Gothic Line itself.