'Sonnenaufgang' was the German third and last major counterattack by Generaloberst Eberhard von Mackensen’s 14^th Army against Major General John P. Lucas’s US VI Corps of Lieutenant General Mark W. Clark’s US 5^th Army in the 'Shingle' beach-head at Anzio on the western side of Italy (16/20 February 1944).

After von Mackensen’s 'Fischfang' first offensive of 3/4 February had taken the Aprilia Factory and Carroceto on the road linking Anzio with Albano in the Alban hills, Lucas had relieved Major General W. R. C. Penney’s battered British 1^st Division with Major General William W. Eagles’s US 45^th Division, and as it arrived from the Garigliano river front, Lucas brought Major General G. W. R. Templer’s British 56^th Division into the line on the 45^th Division’s western flank so that the Albano road sector was held by completely fresh troops. Major General Lucian K. Truscott’s US 3^rd Division remained in the Cisterna sector, which had not yet been seriously attacked.

Generalfeldmarschall Albert Kesselring, the Oberbefehlshaber 'Südwest' and commander of Heeresgruppe 'C', and von Mackensen both looked carefully at the front before deciding where to deliver what they hoped would be their decisive counter-offensive. The two coastal sectors provided most cover, but the German experience at Salerno made them avoid any axis within easy range of the supporting gunfire of Allied warships. Moreover, they wished to make the best use they could of the considerable armoured strength which Adolf Hitler had now made available to them. The two local commanders therefore decided that the optimum axis was the line of the road linking Anzio and Albano. Their plan was to attack initially with four divisions on a very wide front extending on each side of the road, complemented by diversionary attack on the extremity of each of the Allied lodgement’s flanks. As soon as they had achieved a break-in, the Germans would exploit with a concentrated attack by Generalmajor Hans Hecker’s 26^th Panzerdivision and Generalmajor Walter Fries’s 29^th Panzergrenadierdivision.

As he inspected von Mackensen’s plan, Hitler demanded that the main attack should be made on a much narrower front, on each side of the road between Anzio and Albano and thus on the same sector of the front on which the 'Fischfang' and 'Morgenröte' (ii) undertakings of 3/4 and 7/9 February had been attempted, and that the attack should be spearheaded by the Infanterie-Lehr-Regiment, a unit in which he had great faith. The Luftwaffe was to provide maximum support, and was specially reinforced for this purpose, and a notably heavy concentration of field artillery was assembled. A new battlefield weapon was to be used for the first time: this last was the Goliath remotely controlled miniature tank filled with explosives, a weapon intended as a device to help clear a way through the Allied barbed wire and minefield defences.

The Germans were very optimistic about their chances of success, but the general air of confidence engendered in the troops by the concentration of German strength and Hitler’s assurances of inevitable victory had two unfortunate consequences: prisoners betrayed the date of the offensive to Allied interrogators; and when the offensive was defeated the despondency of the German forces was that much greater.

'Sonnenaufgang' was committed in daylight on 16 February because the assault divisions, only newly arrived in the area, lacked the knowledge of the terrain required for a night assault. The Germans launched probing assaults all along the front held by the British 56^th Division and US 3^rd and 45^th Divisions, and then the Allied formations withstood the intense artillery and air attacks before driving back most of the armour and infantry attacks during the first day. German bombers and long-range guns struck at the rear areas in a fruitless attempt to panic the administrative echelons, and in return the Allied air forces were switched from Cassino and flew about 500 sorties mainly against Carroceto and the Aprilia Factory, which the Germans were using as main assembly areas.

During the night the position changed dramatically. Infiltration on each side of the Albano road led to the appearance of a significant gap between the central and left-hand regiments of the 45^th Division. The Germans soon found this gap, and quickly set about widening of the breach still farther during the morning of the offensive’s second day. In the course of the afternoon, von Mackensen came to believe that the moment had come to commit a larger force of fresh troops. Supported by Panzergrenadier battalions, the Infanterie-Lehr-Regiment launched an all-out attack down the Albano road as the core of a major effort involving some 14 German battalions in widening the salient driven into the 45^th Division’s front. Packed into a small area and unable to make any effective use of their armoured strength off the road, however, the German attack provided an excellent target to the massed artillery of the VI Corps, the guns of the Allied warships lying offshore, and Allied warplanes. Despite the extreme severity of their losses, the Germans continued to launch successive attacks in a desperate endeavour to break through.

Lucas ordered the 1^st Division to move out of corps reserve into a blocking position astride the Albano road on the lodgement’s 'final' defence line, and also ordered the 45^th Division to undertake a night counterattack on the salient which the Germans had driven into the Allied front. Right through the second night of the offensive, the Germans moved up more units for a decisive effort on the following day. They drove back the 45^th Division’s counterattack and infiltrated both into and round the US and British positions blocking their advance. At dawn, profiting by the confusion caused by their night’s work and taking the 45^th Division off-balance after its unsuccessful efforts of the night, five German regiments including the Infanterie-Lehr-Regiment reopened the offensive. The weather prevented the Allies' medium and heavy bombers from intervening, but the artillery and fighter-bombers once again provided the Allied defence with very effective support. Most of the 45^th Division was driven back to the 'final' defence line to the east of the Albano road, and the 1^st Division came under attack astride the road itself.

During the afternoon of this day Generalmajor Hans Hecker’s 26^th Panzerdivision was committed, and only the demolition of a bridge over the Carroceto stream prevented a German breakthrough. By the evening the stubborn defence of the 1^st and 45^th Divisions was finally telling on the Germans, who started to pull back for a measure of reorganisation. The fighting went on for two more days in which Major General Ernest N. Harmon’s US 1^st Armored Division and the 1^st Division counterattacked with some success. On 20 February a last despairing effort by the Panzergrenadier divisions came to nothing, and this failure marked the effective end of the last German counter-offensive. The Germans had learned what the Allies had been experiencing for some time, but were still refusing to admit: a winter attack, when armour and heavy weapons are confined to the roads, is extraordinarily difficult and costly. At Anzio 10 German divisions had failed to break through 4.5 Allied divisions, had once more suffered under the hammer of Allied air and artillery superiority, and had their morale severely tested and in fact weakened.