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