At Anzio, the Allied troops were dug in and facing the 16th Panzergrenadier Division. But although the Allies commander, Lucas was replaced by the far more aggressive Major-general Lucian Truscott at the end of February. The Allied troops were unable to make any further headway.
Kesselring knew all he had to do was hold on. He fully expected another amphibious landing north of Rome, this was impossible as the Allies forces were gathering their forces in England for Normandy.
For the next couple of months, their was little activity except in the air where Allied bombers and fighters attacked road and rail targets in northern Italy to disrupt German communications and supplies. In return, the Germans plastered the Anzio position with their 280mm K5 (e) railway gun 'Leopold' which they concealed inside a tunnel in the Alban hills. It became known as Anzio Annie and now resides in an American museum.
During April, both sides poured reinforcements into their positions for the coming struggle for the Gustav line. The bulk of the Eighth Army, under the command of Lieutenant-General Sir Oliver Leese (Montgomery was back in England preparing for the Normandy Invasion), was transferred to the Cassino front. This left just a couple of Divisions to hold the line on the Adriatic coast. These forces included Major-general E. M. Burns' Canadian I Corps, Lieutenant-General Wladislaw Anders' Polish II Corps and Lieutenant-General Sidney Kirkman's British XIII Corps, with Lieutenant-General Sir Richard McCreery's X Corps held in reserve to tie the Germans down. These were welcome reinforcements to Keyes' US II Corps and the French Expeditionary Corps.
On the other side, the Germans had the tenth Army under General Heinrich von Vietinghoff-Scheel, which comprised the XIV Panzer Korps, LI Mountain Corps and Heidrich's 1st Parachute Division still holding Cassino itself. At Anzio, the German 14th Army surrounded Truscott's VI Corps.
The battle opened at 11pm on 11 may with a massive bombardment by over 1,600 artillery pieces along the whole Garigliano-rapido line. By chance, Kesselring's two subordinates were on leave in Germany. Kesselring was taken completely by surprise, the two subordinates were flown back by the first plane.
Four minutes after the barrage opened, it ceased. XIII Corps surged across the Rapido south of Cassino even though many of their assault boats capsized. They rapidly established a bridgehead among the minefields, trenches and barbed wire on the far bank but Anders' Poles on their right to the north of Cassino were less lucky. Hammered by intense German fire as well as slowed down by the steep and rocky mountain sloops covered with thorny bushes, they were unable to make much headway. After suffering nearly 20 percent losses, they were pulled back twelve hours later to recover.
XIII Corps initial success was marred by the fact their engineers only managed to build two bridges across the river on the first day, and a third on May 13th. By then, the French Moroccan and Algerian troops stormed across the Garigliano on the left flank of XIII Corps. By the time the third bridge was up, the French troops had driven the 71st Infantry Division back nearly five miles, causing very heavy casualties.
By May 16th, Kesselring started to withdraw but still held onto Monte Cassino. It was not until the night of the 17th that the Polish troops attacked again, threatening to outflank the town form the north, and Kesselring ordered the 1st Parachute Division to withdraw.
Once a Polish patrol took out several positions occupied by the 1st Parachute, the Polish commander Anders' fed a whole assault into the position and after fighting throughout the 17th with bayonets, grenade and submachine gun, the Poles held the position.
On the morning of May 18th, Anders' ordered a general assault and the surprised Poles walked into the dusty rubble which the paratroopers had evacuated.
At Anzio, Truscott was told by Alexander to make an attempt to break out while the Fifth and eighth Armies charged up the coast toward him from the Gustav line, once out he was to head for the Alban hills and block off the retreat of the German Tenth Army.
The attack began on the night of May 23rd but the Germans stubbornly held onto Cisterna until the 26th. By now the Canadian I Corps had breached the Dora line and Kesselring was in retreat again. the German Fourteenth Army held up Truscotts' advance long enough to allow the Tenth to escape.
May 25th, advance patrols from II Corps bumped into men form the VI Corps reuniting Clarks fifth Army.
May 30th, the Texan 36th Division broke through to the east of the Alban hills, threatening to cut off the Germans there.
On June 2nd, Kesselring asked Hitler for permission to abandon Rome. Hitler agreed and the Germans fell back to the Gothic Line, North of Rome. Rome was entered by Clark's Fifth Army on the 4th June.