The campaign in the Cotentin Peninsula (6-30 June 1944) was the first major Allied advance after the D-Day landings, and ended with the capture of the port of Cherbourg, seen by the Allies as one of the most important objectives of Operation Overlord. The capture of a major port was seen as an essential part of the post D-Day build-up in France, and the seaborne assault had been extended west to Utah Beach to allow for an early advance towards Cherbourg. The Germans did not expect the Allies to land on the eastern coast of the Cotentin because they had flooded large areas of low lying ground, both just behind the beaches and along the Merderet River in the centre of the peninsula, and so the coastal defences on Utah Beach were some of the weakest in Normandy.
This would prove to be a major error. Early on 6 June the 82nd and 101st US Airborne divisions were dropped into the area between the coast and the Merderet, with orders to seize the western end of the causeways across the inundations behind the beaches and to seize and defend the line of the Merderet. The airborne landings didn't go as planned, and instead the American paratroops found themselves scattered across the Cotentin in hundreds of tiny detachments, but eventually enough larger groups came together for them to achieve their most important objectives, allowing the 4th Division to advance inland from Utah Beach. The scattered landings also caused a great deal of confusion behind the German lines, and prevented the commanders on the spot from mounting an effective counterattack on D-Day.
On the first few days after D-Day the American troops on the Cotentin might have been vulnerable to a major counterattack launching using troops brought up from Brittany if one could have been launched before the capture of Carentan on 12 June closed the gap between the Utah and Omaha Beach landing zones. Once again the confusion caused by the scattered airborne landings helped the Americans. General Dollman, commander of the German 7th Army, didn't realise that there had been a landing on the east coast of the Cotentin until late on D-Day, and so the troops in Brittany weren't ordered to move until nearly 11pm. They were unable to move until the following morning, and then came under constant heavy attack from Allied aircraft. More confusion was caused when a large flight of American aircraft dropped dummy paratroops west of St. Lô. This convinced Rommel that a second seaborne invasion was about to hit the west coast of the Cotentin and on 7 June he ordered all available reinforcements to move to that area, to the south west of the real battle. This order remained in place until the morning of 8 June, by which time German communications were in chaos and the units involved were out of touch.
This confusion probably saved the 82nd Airborne from defeat, for on the night of 6-7 June that division was under constant heavy pressure and might have been hard pressed if fresh troops had arrived from Brittany that night. Early on 7 June reinforcements arrived by glider and supplies were parachuted into the area, and at 10am contact was made with the seaborne 4th Division. Soon after that the glider-borne infantry was able to take up a line on the Merderet River, holding that line against a day of German attacks. By the end of D-Day+1 General Collins' VII Corps had captured a bridgehead 8 miles deep and 9 miles wide, and by the morning of 9 June the 82nd and 101st airborne divisions had advanced west and south across the worst of the inundations. Any further advance into the Cotentin was then delayed until the fall of Carentan, which was finally captured by the 101st Airborne on 12 June.
By 12 June the Americans were winning the battle of the build-up in the Cotentin. The Germans now had three divisions in the peninsula, although one had already lost 4,000 of its 10,555 men. In contrast the Americans had the original 4th Division, the reinforced 82nd and 101st Airborne Divisions, the 9th and 90th Division had already landed and the 79th Division was crossing the beaches. In addition they had one of the few senior commanders who didn’t find the bocage country restrictive – 'Lightning Joe' Collins – who had led a division in the jungles on Guadalcanal and New Guinea. Collins was used to operating with limited armour and artillery support. Collins devised an effective tactic for fighting in the hedgerows. Aware that his opponents on the Cotentin had little or no counterattacking potential Collins advanced with his regiments in columns of battalions, each with a 1000 yard frontage. The lead battalion was relieved two or three times each day, so every part of the regiment was used, but none for too long.
On 12 and 13 June Collins attacked at the northern and western ends of his beach head. On both days his troops entered the town of Montebourg, on the road to Cherbourg, only to be repulsed, but in the south they crossed the Douve seven miles to the west of St. Lo and built a bridge over the river. This move convinced Rommel that Collins was about to launch an offensive south-west across the peninsula, and early on 14 June he ordered all available troops to move to the Douve to defend against that attack.
In fact Collins was planning to attack much further north, towards St. Sauveur le Vicomte. On 14 June the US 9th and 82nd Divisions began the attack, and over the next 48 hours they advanced five miles. On 15 June Dollman reported to Rommel that the line of the Cotentin resembled a bow at breaking-point, and during the morning of 16 June the bow snapped. The 82nd Division crossed the upper Douve at St. Sauveur and the 9th crossed further north. The Germans had lost the last line of natural defences between the Americans and the west coast. On the following day the 9th Division advanced six miles, and by the end of the day the Americans could see the coast. As the 9th Division advanced west Collins fed fresh troops into the line to defend their northern flank, and on the night of 17-18 June these troops fought off an accidental German counterattack.
This counterattack was a result of direct interference by Hitler. By 16 June the German forces on the Cotentin had been split into two battle groups. General von Schlieben, with the 709th and part of the 77th Divisions, had orders to defend the direct route to Cherbourg through Montebourg, while General Hellmich, with the 91st and 243rd Divisions was ordered to stop the Americans reaching the west coast and if that failed to prevent them breaking into Brittany. The American advance threatened to drive a wedge between the two battle groups. General Dollman ordered von Schlieben to send the 77th to help Hellmich and to withdraw the rest of his troops into the fortress of Cherbourg. This was the only course of action that might had delayed the fall of Cherbourg, but Hitler intervened and refused to allow any troops to move back towards Cherbourg or to leave their current positions. Even when Rommel pointed out that this would allow the Americans to capture Cherbourg by advancing between the two battle groups Hitler refused to budge.
Early on 17 June he changed his mind, and gave Schlieben permission to make a fighting withdrawal under enemy pressure. Later that day he came close to re-imposing his 'stand fast' order, and then in a rage drew a new line across the peninsula, from St. Vasst de la Hogue on the east coast, through Le Thiel, to Vauville. This thirty mile long line was three times longer than the line Schlieben was already struggling to hold, and included large areas of no value to the defence of Cherbourg. Worse, Schlieben would only be allowed to retreat to this line after fighting for as long as possible at Montebourg, and would have no time to organise the defence of the port.
While Schlieben was struggling to hold Montebourg, Hellmich, reinforced by the 77th Division, attempted to move south into a position from where he could block the American advance to the coast, not realising that the Americans had already advanced west past his intended position. It was this movement that produced the accidental counterattack, when Hellmich's men ran into the northern flank of the advancing American forces. Most of his column was destroyed or dispersed, although 1,200 men did escape along the coast road.
On the morning of 18 June that route was closed when the US 9th Division reached Barneville. The moment his men reached the coast Collins moved them into a new line facing north, with the 9th on the west coast, the 79th in the centre and the 4th Division in the east. One of the reasons Collins was so successful in Normandy and the Cotentin was that he seldom wasted time, and at 3am on 19 June, while the Germans were still watching the west coast, his 4th Division advanced silently towards Montebourg. By the time the Germans realised what was happening their line had been broken, the town was almost surrounded and von Schlieben's men were in full retreat. By the end of the day the Americans had reached Valognes, and by the evening of 20 June they had reached Hitler's last stand line.
The campaign in the Cotentin was about to turn into the battle of Cherbourg. On 21 June von Schlieben ignored a formal call for surrender, and on the following day the American attack began. Their advance was slow but steady, and despite determined German resistance the American had control of the city by 26 June, when von Schlieben was captured. The Arsenal surrendered on the next day and the last naval fortresses on the mole on 29 June. The last resistance on the Cotentin, at Cap de la Hague, the north-western tip of the peninsula, ended late on 30 June, and the campaign in the Cotentin was over.
The port of Cherbourg, the main target of the entire offensive, had been comprehensively devastated by the Germans. Sunken ships and hundreds of contact mines blocked the harbour, while the facilities had been damaged or destroyed. No traffic was possible for three weeks, and it would take months for the port to be reopened. Despite this disappointment the capture of Cherbourg did have two important results. The Allies realised that the German-held ports in Brittany would probably be equally badly damaged, and most of their garrisons were simply left to wither on the vine, not surrendering until the end of the war. In contrast the Germans realised that even their strongest fortresses could be captured relatively quickly by the Allies, meaning that they could not be used to limit the Allied build-up on the continent.