​​The First Canadian Army and the British 21st Army Group had crossed the Seine and were clearing the remaining German troops as the Allies advanced east. The Canadian forces had pushed north from Rouen to Dieppe. A small number of British units had been attached to the First Canadian Army to assist the task.

​The 49th and 51st Infantry Divisions moved westwards and towards the area of Le Havre. They had begun to surround the city and the port. On 5 September the pre-bombardment for Operation Astonia started with multiple bombing raids hitting the city and the defences. This intensified, and on 10 September the Royal Navy joined the fight, with ships HMS Warspite and HMS Erebus and their up to 38cm guns. 

​The support of the British Royal Air Force (RAF), Royal Navy and the 4th and 9th Army Group Royal Artillery saw a vast amount of ammunition bought down on the defences all around the city. A large RAF raid saw over 1,800 bombers drop nearly 10,000 tonnes of ammunition. At 17:45 on 10 September, the Royal Navy ships opened fired on coastal defences and a final RAF raid saw a further 5,000 tonnes of bombs dropped. To the east of Le Havre units of the British 49th Infantry Division then began to assault the German defence lines and anti-tank ditches. 

​During this further bombardment of defences, the 1st East Riding Yeomanry were tasked to carry out a regimental shoot. The armoured unit numbered around 60 Sherman tanks in total. All tanks were deployed to fire onto targets, and had been ordered to fire 60 rounds each per tank. This was in support of the artillery and saw around 3,600 rounds fired by the tanks onto German positions. 

​On 11 September the attack continued as the British forces liberated the villages to the outskirts of Le Havre. This forced any remaining German forces back to the outer defences of the city. By 12 September, both the 49th and 51st Infantry Divisions had entered the city, and it was now the task to clear the remaining German troops. At 11:45 the German commander of the garrison surrendered to the British forces and the city of Le Havre was finally liberated. This also signalled the liberation of the region of Normandy as it was the last place to be liberated in the region where the Allies had landed on the 6 June 1944.​