'Astonia' was the British undertaking by Lieutenant General J. T. Crocker’s British I Corps of Lieutenant General H. D. G. Crerar’s Canadian 1st Army within Field Marshal Sir Bernard Montgomery’s Anglo-Canadian 21st Army Group to establish a bridgehead over the Seine river downstream of Rouen to facilitate the capture the major port of Le Havre, which was seen as an objective of great importance as it was thought to be capable of handling some 20,000 tons per day (12 September 1944).
By this time other Allied forces had pushed through to take the more significant harbour facilities at Antwerp, which were also closer to the fast-moving Allied front line. Le Havre was protected by outlying forts, a deep anti-tank ditch and major field fortifications all covered by minefields and flooded areas, and was held by a garrison of just under 12,000 men, well provided with artillery (although many of the 28 artillery positions in Le Havre could fire only out to sea), under Oberst Eberhard Wildermuth, who had replaced the previous incumbent, Generalmajor Hans Sauerbrey, only on 14 August. The most effective part of the defence was provided by one battalion of the 36th Grenadierregiment of Generalleutnant Erwin Sander’s 245th Division.
On 4 September Major General E. H. Barker’s 49th Division and Major General T. G. Rennie’s 51st Division closed round the perimeter of Le Havre and called on the commander of the garrison to surrender. The German general refused, and the British prepared for the land assault as the German defences were taken under naval and air bombardments. The country behind Le Havre’s main town and harbour rises steeply to high ground which extends to the sheer cliffs of Cap de la Heve and the north coast. The valleys of two rivers, the Lézarde on the west and its tributary the Fontaine, divide the ground into two plateaux: between the Lézarde and the Fontaine is the 'northern plateau', and west and south of the latter is the 'southern plateau', overlooking the town and harbour and, about 3 miles (5 km) inland, covered by the Forêt de Montgeon. Starting from the Lézarde valley where it passes Montivilliers and continuing to the coast near Octeville was a wide and almost unbroken anti-tank ditch, strengthened by extensive belts of mines and wire, and covering numerous fieldworks and strongpoints based on concreted bunkers. From the crest of the southern plateau two forts shielded the town and harbour entrance, and on the coast near Cap de la Heve the Grand Clos battery threatened approaching ships.
The German garrison, which Allied intelligence under-estimated at some 8,700 men (including 4,000 artillerymen, 1,300 naval personnel and 3,400 infantry of varying quality, including the former security and fortress troops such as 5th Sicherungsregiment and the 81st Festungsabteilung, both of very low fighting value), was well equipped with artillery and mortars; the conformation of the ground and the German defences made it a difficult position to capture.
Naval and air bombardments to soften the defences began on 5 September. The monitor Erebus opened fire with her two 15-in (381-mm) guns, but was herself hit by fire from the 375-mm (14.76-in) gun of the Grand Clos battery, and had to withdraw for repair. On the same day the aircraft of Air Chief Marshal Sir Arthur Harris’s RAF Bomber Command attacked the south-western part of the town, in which it was believed the garrison had its headquarters. On 6 September the defence works on the southern plateau were bombed heavily and some two days later so too was the north-western part of the town, a total bomb weight of some 4,000 tons being dropped.
Heavy rain interrupted all operations on 9 September but then weather then cleared, and although the sodden ground delayed the start of the ground attack, naval and air bombardment was resumed on 10 September. After 60 aircraft of RAF Bomber Command had attacked the Grand Clos battery, the monitor Erebus, this time accompanied by the battleship Warspite with eight 15-in (381-mm) guns, opened fire and the battery was soon silenced. Bomber Command made two further heavy attacks during the day in which nearly 1,000 bombers dropped some further 4,900 tons on the defences.
Meanwhile a strong counter-battery shoot by the divisional artillery, strengthened by two heavy and six medium regiments of the 4th and 9th Army Groups of the Royal Artillery, reduced the strength of the German defences still further.
Almost as soon as the last heavy bomber attack finished at 17.30 on 10 September, the divisions of the I Corps began their attack, which continued through the night. The 49th Division, with Brigadier W. S. Clarke’s 34th Tank Brigade under command, set out from the north-east to capture the defences of the northern plateau, subsequently crossing the Fontaine valley to gain a bridgehead on the southern plateau below the Forêt de Montgeon. Flail tanks of the 22nd Dragoons of Major General Sir Percy Hobart’s 79th Armoured Division had first to breach the extensive minefields and, working under German fire in darkness and on rain-sodden ground, 34 flail and two command tanks became casualties; in the attack on strongpoints which followed, six Armoured Vehicles Royal Engineers were also put out of action.
Yet steady progress was made and at midnight, using 'artificial moonlight' (searchlights reflected off the undersides of the clouds), the 51st Division and Brigadier H. B. Scott’s 33rd Armoured Brigade came in on their right attacking from the north. The breaching of minefields in semi-darkness and the crossing of the anti-tank ditch was difficult, dangerous and slow work but by early morning the advance was steadily gaining ground.
During 11 September, with further support by bombers and rocket-firing Hawker Typhoon fighter-bombers, the 49th Division took the defences of the southern plateau, overcame strongpoints in the Harfleur area, and began to advance westward through Le Havre. By nightfall the division had reached Fort de Tourneville.
Meanwhile the 51st Division had cleared the Forêt de Montgeon, taken Octeville, cleared the high ground nearly to Cap de la Heve, and forced its way into the outskirts of Le Havre to attack Fort St Addresse. The battle was resumed on 12 September. The Fort de Tourneville surrendered during the morning and the wounded garrison commander gave himself up. Fort St Addresse surrendered at about 15.30 and when all mopping up was completed more than 11,300 Germans had been taken prisoner. The British casualties amounted to under 500.
The Germans' systematic demolitions in the harbour had been thorough that although clearance was begun at once, shipping could not use the port until 9 October.