'Avonmouth' was a British and French unrealised plan for a landing at Narvik in the far north of Norway to support the Norwegian forces in the area should the Germans launch an invasion of Norway (1939/40).

This plan reflected in particular the British fears of the effect on the Allies' strategic position should the Germans secure Norway’s lengthy coastline, providing them with year-round capability to ship Swedish iron ore even when the Baltic was frozen, and protecting egress for their U-boats and surface vessels into the Norwegian Sea and hence the Denmark Strait and the North Atlantic, with potentially disastrous effects on Allied convoys plying across the North Atlantic with desperately war matériel from the USA.

The key elements of the 'Avonmouth' plan were revived after 'Weserübung', in whose 'Naumburg' sub-element Narvik had been reached by the ships Gruppe I, which had departed Bremerhaven on 6 April. The group comprised 10 destroyers of the 'Typ 1934A' and 'Typ 1936' classes (Georg Thiele, Wolfgang Zenker, Bernd von Arnim, Erich Giese, Erich Koellner, Diether von Roeder, Hans Lüdemann, Hermann Künne, Wilhelm Heidkamp [flag] and Anton Schmitt) under the command of Kommodore Friedrich Bonte. Each of these warships carried some 200 men of the 139^th Gebirgsjägerregiment, one of the two infantry regiments of Generalleutnant Eduard Dietl’s 3^rd Gebirgsdivision.

After the initial landing, the German tactical position was decidedly difficult as the 1,900 mountain troops were outnumbered. However, after the German destroyers had been sunk in the two naval 'Battles of Narvik', about 2,600 German sailors joined the land force, and another 290 German specialists arrived overland via Sweden posing as health care workers. Finally, the Germans were reinforced by about 1,000 men air dropped over Bjørnfjell in 'Büffel' (i), bringing the German strength to some 5,000 men. The German position veered between good and bad several times, and on occasion the entire operation was controlled directly from the German high command in Berlin, where Adolf Hitler’s mood apparently swung heavily and he repeatedly contemplated withdrawal.

Intelligence agents captured later in the war also revealed that Dietl had considered a retreat by his force eastward to the Swedish frontier for internment in neutral Sweden.

The Norwegian forces, based on Major General Carl Gustav Fleischer’s 6^th Division, reached a strength of between 8,000 and 10,000 men after a few weeks, and the overall number of Allied troops involved in and around Narvik eventually reached 24,500 men.

The early phase of the German invasion had the advantage of operational and tactical surprise. The Norwegian troops in northern Norway had been called out on a three-month neutrality watch during the winter of 1939/40, and had thus trained together. Between 9 and 25 April, however, the Norwegian forces suffered three major setbacks. Firstly, the forces protecting Narvik were unable to resist the Germans as a result of the fact that the local commanding officer, Colonel Konrad Sundlo was a Quisling and refused to mount any defence; secondly, about 200 of the Narvik garrison’s men, who had escaped capture and were blocking the railway to Sweden, were taken by surprise while resting at Bjørnfjell, most of them being captured; and thirdly, the 1/12^th Regiment sent to hold Gratangsbotn was attacked by surprise while in camp, its resulting loss of morale effectively rendering it useless for the rest of the campaign.

The Norwegian plan for a counterattack, under the immediate command of Colonel Kristian Løken, on the German beach-head around Narvik had been based on pushing toward Elvegårdsmoen and Bjerkvik through Salangsdalen over the Lapphaugen hill, believed to be held by only one German company, with the 2/15^th Regiment in a frontal attack with artillery support. It was also planned that the 1/12^th Regiment would advance on the Germans' main positions in Gratangsbotn by a surprise march across difficult terrain over Fjordbotneidet. The independent Alta Battalion was in divisional reserve and sited to support the 1/12^th Regiment. On 24 April the 2/15^th Regiment began its attack on Lapphaugen but a combination of dire weather and German resistance defeated the Norwegian effort. Even so, the Germans decided to abandon their positions on Lapphaugen and Gratangsbotn, and in foul weather the 2/15^th Regiment did not appreciate the fact and therefore did not press its advance. In almost blizzard conditions the 1/12^th Regiment crossed the Fjordbotneidet and reached Gratangsbotn to find the area clear of Germans. Exhausted after the forced march, the Norwegian troops went to rest in the farmhouses and barns in Gratangsbotn.

For reasons not fully explained, but probably a misunderstanding by Major Nils Christoffer Bøckman, its commanding officer, the 1/12^th Regiment did not post a sufficient perimeter defence, a fact made all the more critical by the fact of Gratangsbotn’s location in a bowl dominated all round by high ground. The Germans did not miss this opportunity and immediately counterattacked with a force of 165 men. Though inferior in numbers, the Germans suppressed the surprised Norwegians with their superior firepower, notably mortars and heavy machine guns. Some 34 Norwegian soldiers were killed, 64 wounded and 130 taken prisoner, the officer losses being especially heavy: three out of five company commanders were killed and one was wounded in the fighting, while the fifth was snow-blind and did not take an active part in the battle. The Germans suffered only six soldiers killed, 16 wounded and three missing. The surviving Norwegians retreated from Gratangsbotn, and were later reorganised as a reduced battalion with two rifle companies and one support company.

Despite their victory at Gratangsbotn, the Germans understood that their position in Gratangsbotn was untenable. The fresh Alta Battalion under Arne Dagfin Dahl pressed on from the north and the 2/15^th Regiment resumed its advance over Lapphaugen. So as the Norwegian pressure on them mounted and their supply situation became increasingly threatening, the Germans abandoned Gratangsbotn and withdrew from Lapphaugen hill and the Gratangsdalen valley.

In the first days of May, the Norwegians started an advance south toward Narvik. Once it became clear that the Allies would launch a major landing at Narvik in mid-May, the Norwegian shifted their axis of advance toward Bjørnfjell.

The first British troops had arrived and established their headquarters in Harstad on 14 April. In the following days, three battalions were deployed mainly at Sjøvegan, Skånland (where a naval base was established) and Bogen. Later, they were deployed south of Ofotfjord, at Ballangen and Håkvik. This initial British detachment was reinforced by Général de Brigade Marie Emile Antoine Béthouart’s French 1^st Division Légère des Chasseurs comprising Lieutenant-Colonel Valentini’s 27^th Demi-Brigade des Chasseurs Alpins (three battalions) and Lieutenant-Colonel Magrin-Verneret’s 13^th Demi-Brigade de Légion Étrangère (two battalions). This French group landed at Ankenes, Bjerkvik, Elvenes and Foldvik between 28 April and 7 May.

On 9 May four Polish battalions were delivered, and were first deployed north of the fjord before being moved to the area south of the fjord. Early in June these battalions were grouped as Général de Brigade Zygmunt Bohusz-Szyszko’s Polish 1^st 'Carpathian' Demi-Brigade des Chasseurs Alpins, otherwise the Samodzielna Brygada Strzelcow Podhalanskich (Polish Independent Highland Brigade).

The French troops were initially deployed both north and south of the Ofotfjord, but later the north would be the main French area of operation as the four Polish battalions deployed to the area south of the fjord after an initial grouping to its north. Despite their growing numerical advantage over the German force in the Narvik area, the Allies had considerable difficulty in deciding how best to retake Narvik and sever the railway used to transport iron ore from Sweden. Not least of these difficulties was the lack of any unified command for the forces facing the Germans: the Norwegians and Allies retained separate commanders, and co-operation between them was not always smooth. Even within the British forces, the army and navy commanders, Major General P. J. Mackesy and Admiral of the Fleet the Lord Cork and Orrery, had difficulty co-operating: Cork advocated a swift and direct attack from the sea, while Mackesy advocated a cautious approach from both sides of the Ofotfjord. It was only on 21 April that Cork was given command of all the Allied forces.

During the second week of May, the Norwegian advances against the Germans east of Gratangseidet were the most significant movements on the Narvik front. In addition, on the Norwegian right flank French alpine troops advanced up the Laberg valley with the support of a company of Norwegian ski troops. In the south, the Allies did not have much success, and in the north of the Ofotfjord they were static. The Norwegians continued their successful mountain campaign, and in mid-May the Allies took the initiative and achieved significant victories.

Both Paris and London had been growing impatient with the slow progress in Narvik, and Béthouart was pressing for more urgent action. The cautious approach on land was abandoned and an amphibious attack was launched at about midnight on 12 May. This was directed at Bjerkvik and preceded by a bombardment from British warships in the Herjangsfjord. Then landing craft put ashore the French legionnaires supported by five French light tanks. The French took Bjerkvik and the Elvegårdsmoen army camp, and advanced to the north-east into the area from which the Germans were withdrawing and south along the eastern side of the Herjangsfjord. The plan also required Polish troops to advance overland toward Bjerkvik on the western side of the fjord, but the difficulty of the terrain delayed them so badly that they arrived only after Bjerkvik had been taken. It had also been part of the plan for French and Norwegian troops to advance from the north in order to trap the Germans, but co-operation problems between the Norwegian and French commanders left a gap through which the Germans escaped. Despite this, the Allies had a clear path north of Narvik and planned to attack over the Rombaksfjord.

It had been anticipated in London that as the build-up of troops in Narvik continued, a corps headquarters would be needed to exercise effective control, and on 11 May Lieutenant General C. J. E. Auchinleck arrived in Narvik. Under Cork’s overall command, Auchinleck on 13 May assumed command of the Allied land and air forces, which at this time became designated as the North-Western Expeditionary Force. It was clear to the Allies that once Narvik had been captured, its long-term retention would depend on the permanent retention of Bodø to the south in Nordland, which controlled the only major route available to the Germans for any advance from Trondheim.

Consequently, Auchinleck redeployed all British troops to concentrate on this southern enterprise, and appointed Béthouart, an expert in both mountain and winter warfare, to command the French and Polish troops who would be responsible for operations in the Narvik area in conjunction with Norwegian forces.

Again, the Allies delayed their attack on Narvik itself as they waited for air support to be fully established from the airfield at Bardufoss. At 23.40 on 28 May, a naval bombardment began from the north to prepare the way for the start of 'Avonmouth' proper as one Norwegian and two French battalions were transported across the Rombaksfjord for an advance on Narvik. In the south, the Polish battalions were to advance toward Ankenes and the inner part of the Beisfjord. The maximum capacity of the landing barges was 290 men and these troops could not be reinforced for 45 minutes, but the first troops to be transported were able to get a foothold on Ornes by the time the rest of the French and the Norwegians were landed. The French moved west toward the city and east along the railway. The Norwegians moved toward Taraldsvik mountain, circled around and moved down toward the city.

The German commander had decided before 07.00 to evacuate Narvik and withdrawn along the Beisfjord. It seemed now that it was only a matter of time before the Germans would be compelled to surrender. They were pushed from the north by the Norwegians, from the west by the French and from the south-west by the Poles, and it seemed that Bjørnfjell would be the Germans' last stand. But events elsewhere in Europe came to their rescue. London had already secretly decided, on 24 May, to evacuate the British troops from Norway, and this became apparent in the following days.

During the night of 24/25 May, Cork received orders to retreat, but under cover so the Germans would be prevented from interfering. The Allied commanders agreed that an attack on Narvik would disguise the retreat and allow the destruction of the harbour that was so vital to Germany for the shipment of Swedish iron ore. It was only in the first days of June that the Norwegian government and commanders were first told of the British decision, and the news was met with disbelief and bitterness. The Norwegians still hoped to defeat the Germans alone and, as late as 5 June, one of the two Norwegian brigades was ordered to attack. The Norwegian government also explored the possibility of creating a neutral but free state in northern Norway. This plan was futile, and on 7 June the Norwegian king and his government were evacuated by sea to the UK.

All Allied troops were evacuated from Narvik between 4 and 8 June in 'Alphabet'. Three Polish passenger ships, Sobieski, Batory and Chrobry, took part in the evacuation, and Chrobry was sunk on 14/15 May by German bombers. On 8 June Dietl’s revived forces retook Narvik, and on 10 June the last Norwegian resistance ended.