'Blücher' (vii) was the German operation, in what is sometimes known as the '2^nd Battle of Dunkirk', whereby the Germans attempted to lift the Allied siege of the port of Dunkirk in north-western France (5 April 1945).

The siege had begun on 15 September 1944 when Allied units of Major General C. Foulkes’s (from 10 November Major General A.B. Matthews’s) Canadian 2^nd Division surrounded the German garrison of fortified port of Dunkirk. The siege lasted to 9 May 1945, after the official end of World War II in Europe, and in this time the German units within the fortress withstood only probing attacks as the opening of the altogether larger port of Antwerp in Belgium was deemed altogether more important by Field Marshal Sir Bernard Montgomery, commanding the Allied 21^st Army Group. Montgomery had decided to contain but not to attempt the capture of Dunkirk with Brigadier Alois Liska’s 1^st Czechoslovak Armoured Brigade. The fortress, commanded by Konteradmiral (from 30 September Vizeadmiral) Friedrich Frisius in succession to Generalleutnant Wolfgang von Kluge, commander of the 226^th Division, eventually surrendered unconditionally to Liska on 9 May 1945, one day after the surrender of Germany had taken effect.

General H. D. G. Crerar’s Canadian 1^st Army was operating on the loft of Montgomery’s 21^st Army Group axis of advance and Montgomery had allocated to the Canadian army the task of clearing the French ports along the southern side of the English Channel and then pressing forward into Belgium and the Netherlands. Most of the ports had been fortified and, despite the generally poor quality of their garrisons, the Canadian formation had to take each of them in individual set-piece assaults.

The ports were needed to supply the Allied armies and the lack of such facilities in the north-eastern part of France had halted or slowed much offensive activity. Montgomery had estimated that the English Channel ports would be sufficient for his needs and this view persisted until mid-September. Under orders from General Dwight D. Eisenhower, the Allied supreme commander in Europe, Montgomery modified his instructions to Crerar on 13/14 September, telling him that 'Early use of Antwerp so urgent that I am prepared to give up operations against Calais and Dunkirk' and 'Dunkirk will be left to be dealt with later; for the present it will be merely masked.'

Action against Calais continued in 'Undergo', at least partly in order to silence the heavy artillery sited nearby. The forces that might have been used to capture Dunkirk were released for the 'Battle of the Scheldt' and thus open access to the largely undamaged port of Antwerp. Instead, smaller Allied forces held a perimeter around the Dunkirk.

In the first weeks of the siege of what Adolf Hitler had designated as the Festung 'Dünkirchen', while Allied forces were being deployed on the Scheldt river as part of the operations to take Antwerp, several units were involved in the containment of Dunkirk. Brigadier W. J. Megill’s Canadian 5^th Brigade, part of the Canadian 2^nd Division, was relieved by Brigadier B. W. Leicester’s British 4^th Special Service Brigade, which was in turn relieved by Brigadier J. A. Oliver’s British 154^th Brigade. Most of the siege was the responsibility of the 1^st Czechoslovak Armoured Brigade from a time early in October 1944 until the final surrender. The German garrison comprised a wide variety of men, including navy and air Force personnel, as well as army and fortress units: these included men of the 49^th Division, 97^th Division, 226^th Division, 346^th Division, 711^th Division, two fortress battalions and the 2,000-man Kampfgruppe 'Reinecke' of the Waffen-SS. The total German strength was more than 10,000 men, many of them remnants of five divisions which had been mauled during the Normandy campaign and had then been pulled back to Dunkirk. The town itself was heavily fortified, and well-supplied to survive a lengthy siege.

The Canadians approached Dunkirk from the south-west, and on 7/8 September the Canadian 5^th Brigade captured Bourbourg, about 8.1 miles (13 km) from the town. The German outer perimeter ran through the villages of Mardyck, Loon-Plage, Spycker, Bergues and Bray Dunes, 4.3 to 7.5 miles (7 to 12 km) from Dunkirk. The Calgary Highlanders attacked Loon-Plage on 7 September against very heavy opposition and suffered enough casualties that each of its companies was reduced to less than 30 men. The village was taken on 9 September only when the Germans withdrew. During the following 10 days, Canadian units nibbled at the German perimeter, taking Coppenaxfort on 9 September and Mardyck on 17 September, both of them in the area to the west of the town, Bergues on 15 September and Veurne, Nieuwpoort de Panne, to the east of Dunkirk in Belgium. Bray Dunes and nearby Ghyvelde, both just within France, were taken on 15 September, with air support after initial attacks had failed.

By this time it had become clear that the German defenders were not about to be expelled without a major assault. Given the need to open the Scheldt river estuary to provide access to Antwerp and the likelihood that Dunkirk would therefore become an objective of only limited use as a supply port as a result of its demolition, the major Canadian units were redeployed. Nearby Oostende had fallen easily to the Canadians when the Germans withdrew, and its port was partially opened on 28 September, easing the Allies' supply problems. Dunkirk was therefore no longer worth the cost of its capture.

The task of the Allied forces around Dunkirk was now revised to the containment of the German garrison and the minimisation of their inclination to continue the fight by reconnaissance, artillery and air bombardment and propaganda. Coastal supply routes used by German Schnellboote and air supply drops were also to be severed. Of all of the German fortress garrisons on the English Channel coast, Dunkirk appears to have been the most resilient: the defenders at the other English Channel ports, especially Calais and Boulogne, and the artillery sites at Cap Gris Nez were easily persuaded to surrender, while those in Dunkirk were more determined and capable of mounting an active defence.. The garrison thwarted early probes by the Canadians with sufficient aggression to dissuade them from a full assault. By this stage, other priorities compelled the Canadians to persist in patrolling and local counterattacks. On 16 September, the Canadian 2^nd Division was relieved by the 4^th Special Service Brigade, and during the night of 26/27 September, the 4^th Special Service Brigade was itself replaced by the 154^th Brigade. The Germans attempted to take advantage of the change with sorties against the 7/Black Watch in Ghyvelde and against 7/Argyll and Sutherland Highlanders at nearby Bray Dunes Plage. Both attacks were repulsed but only after the headquarters of the Argyll and Sutherland Highlands had been partially occupied and houses in Ghyvelde had been destroyed. A truce was negotiated from 3 to 6 October, at the initiative of the French Red Cross, to allow the evacuation of 17,500 French civilians and also Allied and German wounded. The truce was then extended to allow the Germans to restore defences that had been removed to allow the evacuation.

On 9 October, the 1^st Czechoslovak Armoured Brigade took over the conduct of the siege. The Czechoslovaks executed frequent raids into the eastern suburbs for nuisance effect and the seizure of prisoners: an attack on 28 October took 300 German prisoners. There was a flurry of attacks and retaliatory counterattacks, mostly on the eastern perimeter, during November 1944. Conditions on both sides were difficult during the winter of 1944/45. The low-lying ground outside the city had been flooded by the Germans to form part of the defences and adjacent land had become water-logged, hampering movement and making life unpleasant. Canadian gunners reported that gun pits needed to be bailed out, the sides of dug-outs collapsed and transport became mired in the mud. Czechoslovak morale was maintained by leave in nearby towns and in Lille. The defenders were stuck with poor food, deficient medical care and harsh discipline.

Undertaken on 5 April, 'Blücher' (vii) was the last German offensive operation in France during World War II as German forces pushed the front back about 9.33 miles (15 km) before digging in and holding as the fighting continued until 4 May.

On 28 April and 2 May 1945 the Germans were able to deliver a limited quantity of supplies to the garrison with some of their 28 Seehund two-man midget submarines. Normally armed with two torpedoes mounted on the outside of the hull, the submersibles were modified for the supply missions with special food containers in place of the torpedoes. On the return voyages the containers carried mail from the Dunkirk garrison.

The garrison surrendered unconditionally to Liska on 9 May 1945, two days after the surrender of Germany had been signed and one day after the surrender became effective.