The capture of the port of Cherbourg was one of the most important early objectives for the Allies after the D-Day landings. The planners for Overlord believed that the capture of an intact major port was essential if they were to be able to build up their forces faster than the Germans, and Cherbourg was the only such port in the Normandy area. The Germans were also aware of this, and had strongly fortified every major port in the possible invasion areas, in the hope that this would allow them to overwhelm the Allies on the beaches.
Cherbourg was defended by General Karl von Schlieben, the commander of one of the two German battle groups that were engaged in the Cotentin campaign. Hitler's interference during the Cotentin campaign meant that von Schlieben was forced to defend a line that ran across the entire peninsula, from St. Vaast de la Hogue in the east to Vauville in the west, instead of being able to concentrate his troops in the strong semi-circle of defences around Cherbourg. He had also been denied permission to make an orderly withdrawal into the defences when it became clear that the Americans were about to reach the west coast of the peninsula, so those troops that did reach Cherbourg had to be thrown into the defences as they arrived. Von Schlieben calculated that he had 21,000 men to defend Cherbourg, made up from the remains of four divisions, naval gunners, flak gunners and workers from the Todt organisation. He reported that he was short of officers, had many low grade troops and one fifth of his men were Russians and Poles. Hitler's refusal to allow an orderly retreat meant that the stockpiles of mortar and artillery ammunition stored in the fortress had been used up before the battle began.
The fortifications of Cherbourg were still formidable. The city was surrounded by a ring of concrete fortifications built onto three ridges that commanded every line of approach. In the city itself the Arsenal was a powerful fortress, and the navy had built forts to defend the harbour. If von Schlieben had been allowed to retreat in good order then these fortifications might have held the Americans up for some time.
The American forces in the Cotentin were commanded by General 'Lightning Joe' Collins. He had three divisions available for the attack on Cherbourg – the 4th, 9th and 79th. It was the 9th Division that reached the west coast of the Cotentin on 18 June, while on the following day the 4th Division had broken through the main German defences on the east coast. By the end of 20 June all three divisions had reached Hitler's 'last stand' line. 21 June was spent reconnoitring the defences, before Collins issued a formal demand for surrender, which von Schlieben ignored.
This was followed by a large scale Allied bombing raid. At about noon on 22 June four squadrons of RAF Typhoons and six squadrons of RAF Mustangs began the attack, followed by all twelve fighter-bomber groups in the American Ninth Air Force and eleven groups from Ninth Bomber Command. Between them the four waves of attacks dropped 1,100 tons on the German defences. Despite this the German defences held firm on 22 June, although after some fierce fighting the Americans did manage to establish footholds on all three ridges. At this stage in the battle each pillbox had to be blasted out, and Collins' men developed a slow but relatively safe method of dealing with these fortifications. Artillery and dive bombers would force the Germans into their concrete defences. A light bombardment would keep them pinned down while the infantry advanced to within 400 yards of the pillbox. The infantry would then take over, pouring heavy fire into the embrasures, while combat engineers worked their way around to the rear, blew the doors open and then threw explosives or smoke grenades into the pillbox.
These tactics meant that the Americans were able to make steady progress on 23 June. By early in the afternoon von Schlieben reported that the Americans had broken through on the land front and were advancing in four wedges towards the city. On the next day he reported that he had committed his last reserves to the battle, including a number of non-combatants equipped with old French weapons. He also handed out a large number of Iron Crosses that had been dropped in by parachute, in an attempt to boost morale. This didn't stop the US 4th Division reaching the northern coast three miles to the east of the city.
On 25 June the 4th and 9th Divisions, with the help of a naval bombardment, fought their way along the coast into the outskirts, while the 79th Division, in the centre, became involved in a two day long attack on Fort de Roule, one of the strongest positions in the defences. On 26 June this position fell, and all organised resistance in the city ended. Von Schlieben was captured, but he refused to order the Arsenal or the naval forts to surrender.
General Sattler, commander of the Arsenal, was less fanatical. On 27 June, when Collins sent his Psychological Warfare Unit to the Arsenal, Sattler indicated that he would surrender if the American tanks would fire a few shells at the fortress. The shells were duly fired, after which Sattler and 400 men marched out with their bags packed! The harbour forts held out for longer, and the last one didn't surrender until 29 June. On the following day the last German troops in the peninsula, at the Cap de la Hague, also surrendered, and the Cotentin campaign was over.
Unfortunately for the Allied the Germans had spend most of the time since D-Day destroying the port. One American engineer described their efforts as 'a masterful job, beyond a doubt the most complete, intensive, and best planned demolition in history'. The outer breakwater had been cratered, the quay walls damaged, essential cranes destroyed, the harbour blocked with sunken ships and hundreds of mines scattered across the harbour. Teams of British engineers spent weeks painstakingly deactivating these mines, while American engineers cleared the physical damage, and the first deep-draught cargo ships were able to enter the outer harbour on 16 July, but it was months before anything like the expected amount of supplies could travel through Cherbourg. Fortunately for the Allies they had dramatically underestimated how much material they could unload over the invasion beaches, through the British Mulberry harbour, and using the smaller ports that fell into their hands almost intact.
The destruction at Cherbourg had an impact on the campaign in Brittany, where the Allied had been planning to capture the ports on the west coast. Instead, assuming that these ports would also be too badly damaged to use, their garrisons were isolated and besieged, and in several cases only surrendered in May 1945.
The speed with which Cherbourg fell demoralised many German generals. Once the original landings had succeeded, and it became clear that the Allies were not going to be swept back into the seas, the Germans knew that they could only win if they could move reinforcements to the front quicker than the Allies. Like the Allies they underestimated how much could be done on the beaches, and believed that the capture of a major port was essential. As a result every major port was heavily fortified, but the fall of Cherbourg made it clear that even the best fortifications could be beaten, and quickly.
The fall of Cherbourg also had another unexpected impact on the Germans, many of whom still believed that the Normandy landing were only a feint, to distract German attention from the 'real' landings, which would come in the Pas de Calais. To these men the fall of Cherbourg marked the logical end of the Normandy campaign and a signal that the main landings were about to begin, and was used as an argument against moving any troops from the Pas de Calais to Normandy.