'Oldenburg' (ii) was the German capture of Oslo, the capital of Norway, by the forces of Konteradmiral Oskar Kummetz’s Gruppe V, within 'Weserübung' (9/10 April 1940).

Gruppe V comprised the heavy cruiser Blücher, the pocket battleship Lützow, the light cruiser Emden, the torpedo boats Albatros, Kondor and Möwe, and 14 minesweepers and smaller vessels, which transported and landed elements of Generalmajor Hermann Tittel’s 69^th Division and Generalmajor Erwin Engelbrecht’s 163^rd Division.

Gruppe V met the most serious resistance at the inner defensive fortifications of the Oslofjord, in the vicinity of Drøbak. Leading the group, Blücher approached the forts on the tactical assumption that these would be taken by surprise and therefore not be be able to make a timely response, like many others in the outer part of the fjord. It was not until the cruiser was at point-blank range that the three 11-in (280-mm) guns of the Oscarsborg fortress opened fire, belying their half-century age and obsolescence by obtaining hits with every shot. Within a matter of minutes Blücher was crippled and burning heavily, and the damaged warship was soon finished off by a salvo from land-based torpedo tubes, sinking the ship, which carried most of the administrative and security personnel intended for the administration of captured Norway, and also the headquarters staff of the army formations assigned to seize Oslo.

Also damaged in the attack and believing the Blücher had entered a minefield, Lützow turned back with the rest of Gruppe V some 12 miles (19 km) to the south toward Sonsbukten, where the embarked troops were unloaded. The distance the troops had to advance delayed the arrival of the main German invasion force for Oslo by more than 24 hours, though Oslo was nonetheless captured less than 12 hours later by troops flown into the nearby airport and base at Fornebu.

The defence of Oslo was provided by the Royal Guards battalion based in Oslo and Elverum, Generalmajor Carl Johann Erichsen’s 1^st Division (1^st, 2^nd and 3^rd Regiments, 1^st Cavalry Regiment and 1^st Artillery Regiment) and Generalmajor Jacob Hvinden Haug’s 2^nd Division (4^th, 5^th and 6^th Regiments, 2^nd Cavalry Regiment and 2^nd Artillery Regiment).

The German plan called for Fornebu to be taken by the airborne assault of a paratroop company of Major Erich Walter’s 1/1^st Fallschirmjägerregiment of Generalleutnant Kurt Student’s 7^th Fliegerdivision before the first air-landed troops were delivered. The delay to the main part of the assault force therefore placed greater emphasis on the need for success in this airborne part of the operation. But adverse weather hit the Oslo transport force, which comprised 29 Junkers Ju 52/3m aircraft. After two of his aircraft had collided in the thick overcast, the transport force commander reluctantly decided to turn back without dropping the paratroopers.

A considerable dispute followed back at base when this information was received by radio, but eventually the air commander ordered all his forces to turn back. At that moment, though, Hauptmann Wagner, in command of the leading element of the transport force, arrived over Fornebu airfield. Suspecting perhaps that the order to turn back was a Norwegian trick, Wagner decided to press on with the original plan. As his aeroplane came in to land it was hit by machine gun fire and Wagner was killed. The co-pilot took over and decided to turn back.

Thus the whole assault force was now on its way back to Germany, despite the fact that one part of it at least had attempted to land the paratroops rather than drop them. Over Fornebu were six Messerschmitt Bf 110 two-engined heavy fighters to support the airborne forces and then land on the captured airfield. Now very short of fuel, their commander decided that the aircraft would land and their rear gunners would attempt to hold off the Norwegians with machine gun fire until another force could be flown in after the weather had improved. One Bf 110 crashed on landing, but the other five got down successfully and adopted the best defensive positions they could.

The crews of the German fighters were then amazed to discover that the Norwegians had pulled out, leaving the airfield in the hands of the German fighters.

By 09.15 a few Ju 52/3m transports arrived and disgorged their paratroops, and throughout the morning other transports arrived, after refuelling, to bring in more paratroops. Yet the German garrison on the airfield was tactically very vulnerable, and was saved only by the paralysis the new German offensive method had inflicted on the Norwegians.

The pilots of the Norwegian fighter wing based at Fornebu resisted with their Gloster Gladiator biplane fighters until they had exhausted their ammunition, and then flew their aircraft to whatever secondary airfields were available. The ground personnel of the fighter wing soon ran out of ammunition for their anti-aircraft guns, and in the general confusion of getting the fighters into the air no one had issued ammunition for the small arms of the ground personnel. Resistance at Fornebu therefore ended quickly, and Norwegian attempts to mount a counterattack came to nothing.

With the arrival of the first elements of the 163^rd Division's 324^th Regiment, the German hold on the airfield became better assured, but the German commander then decided to advance on Oslo with some six companies of infantry, which was by any objective criterion a hopelessly inadequate force. Moving swiftly, and with a military band giving the force the appearance of assured conquerors, the force moved on Oslo, which was immediately declared an open city.

However, the delay in the German occupation of Oslo provided the Norwegians with the time to evacuate the royal family, parliament and national gold reserves to points still out of the reach of the Germans.

While the three major warships whose target was Oslo were supported by the motor minesweepers R 8, R 18 and R 19, there were also four subgroups carrying assault forces for the capture of smaller objectives: the torpedo boat Möwe was directed against Son and Moss, the torpedo boats Albatros (grounded and wrecked 10 April while under fire from Norwegian coastal artillery) and Kondor as well as the motor minesweepers R 7, R 17 (sunk by the Norwegian minelayer Olav Tryggvason and minesweeper Rauma) and R 22 against Horten, the motor minesweepers R 20 and R 24 against Rauøy island, and the motor minesweepers R 22 and R 23 against Bolearne island.

After the appointment of Generalmajor Otto Ruge, the inspector general of infantry, as the Norwegian commander-in-chief on 10 April, the Norwegian strategy was to fight delaying actions against the Germans advancing to the north from Oslo to link with the German forces landed at Trondheim. The primary aim of the Norwegian effort in eastern Norway was to buy the Allies enough time to recapture Trondheim, and start a counter-offensive against the German main force in the Oslo area. The region surrounding the Oslofjord was defended by Erichsen’s 1^st Division, and the rest of the region was covered by Haug’s 2^nd Division. Prevented by the German invasion from being able to implement an orderly mobilisation, the Norwegians sent improvised units into action against the Germans. Several of the units facing the German advance were led by officers especially selected by Ruge to replace commanders who had failed to show sufficient initiative and aggression in the early days of the campaign.

The German offensive to effect a junction of their forces in Oslo and Trondheim began on 14 April with an advance to the north-west and north from Oslo toward the Gudbrandsdalen and Østerdalen valleys, which led to Åndalsnes and Trondheim respectively. Hønefoss was the first town to fall to the advancing German forces. To the north of Hønefoss the Germans began meeting Norwegian resistance in the form initially of delaying actions and later of units fighting organised defensive actions. During intense fighting with heavy casualties on each side, men of the Norwegian 6^th Infantry Regiment blunted the German advance at the village of Haugsbygd on 15 April. The Germans broke through the Norwegian lines at Haugsbygd on the next day only after employing tanks for the first time in Norway. Lacking anti-tank weapons, the Norwegian troops could not hold back the German attack.

However, the basis for the Norwegian strategy had already started to fail on 13 and 14 April, when the 1^st Division’s 3,000 men in Østfold fell back to the east without orders and sought refuge in neutral Sweden, where they were interned. On the same day that the 1^st Division began to cross into Sweden, the two battalions of the 3^rd Infantry Regiment at Heistadmoen army camp in Kongsberg surrendered. Generalmajor Einar Liljedahl’s 3^rd Division, tasked with the defence of southern Norway, surrendered to the Germans in Setesdal on 15 April, having seen no action up to that point. Some 2,000 Norwegian soldier were taken prisoner. With the abandonment on 20 April of the Franco-British 'Boots' plan for the recapture of the central Norwegian coastal city of Trondheim, Ruge’s strategy became for all practical considerations impossible.

With the termination of the 'Boots' scheme to retake Trondheim, British forces which had been landed at Åndalsnes in 'Primrose' and 'Sickle' moved into eastern Norway. By 20 April three British half-battalions had advanced as far to the south as Fåberg, near the town of Lillehammer in the Gudbransdalen. For he most part, the majority of the British units deployed to eastern Norway in April 1940 were the Territorial Army battalions of Brigadier H. de R. Morgan’s 148^th Brigade and the regular battalions of Brigadier H. E. F. Smyth’s 15^th Brigade. In a series of battles with Norwegian and British forces over the next weeks the Germans continued to drive to the north and north-west from Oslo, their main effort through the Gudbrandsdalen. Particularly heavy fighting occurred in places such as Tretten, Fåvang, Vinstra, Kvam, Sjoa and Otta. In the Battle for Kvam on 25/26 April, the British managed to delay the German advance for two days of heavy fighting. Other German units broke through the Valdres and Østerdalen valleys, in the former case after heavy fighting and an initially successful Norwegian counterattack.

During their advance from Oslo, the Germans regularly broke Norwegian resistance through the effective use of tactical air attacks. Junkers Ju 87 dive-bombers proved particularly effective in demoralising the Norwegian forces opposing the advance. The Norwegians possessed almost no anti-aircraft weapons, and this made it possible for the German aircraft to operate with near-total impunity. Likewise, when German tanks were employed, the Norwegians had no effective means to defeat them. The British established the RAF’s No. 263 Squadron on the ice of the frozen lake Lesjaskogsvatnet on 24 April to challenge German air supremacy, but many of the squadron’s fighters were destroyed by German bombing on 25 April. The four Gloster Gladiator biplanes which did survive to be evacuated to Setnesmoen army base near Åndalsnes were out of operation by the end of 26 April. Setnesmoen was bombed and knocked out by the Luftwaffe on 29 April.

After its seizure of Kristiansand on 9 April in 'Karlshafen', the battalion-strong German invasion force in the southern bulge of Norway permitted the evacuation of the civilian population from the city. At the same time the Germans moved to secure the areas surrounding Kristiansand. After several days of confusion and episodes of panic among the Norwegian troops, and despite the complete absence of fighting, the 2,000 men of the defending 3^rd Division in Setesdal surrendered unconditionally on 15 April.

The important western cities of Bergen and Stavanger were captured by the Germans on 9 April in 'Bremen' and 'Stadthagen' respectively . Some 2,000 German soldiers occupied Bergen and captured the Norwegian arms depots there. The small Norwegian infantry forces in Bergen retreated to the east, demolishing two railway bridges and sections of road after them. Despite the loss of the cities, the regional commander, Generalmajor William Steffens, commander of the 4^th Division, ordered the total mobilisation of the units he commanded. During the middle of April, the 6,000-strong 4^th Division, responsible for the defence of western Norway, was mobilised around the town of Voss in Hordaland. The 4^th Division was the only military district outside northern Norway to be mobilised both in its entirety and in an organised fashion. The soldiers of the 4^th Division managed to repulse the initial German push along the railway of the Bergen line connecting western and eastern Norway.

After the units of Generalmajor Jacob Ager Laurantzon’s more northerly 5^th Division had covered the British 'Primrose' landing at Åndalsnes, Steffens planned an offensive for the recapture of Bergen. To achieve this, the 4^th Division had a total mobilised strength 6,361 men and 554 horses. Steffens’s plan was rendered redundant when, on 16 April, Ruge ordered most of the division to be redeployed to Valdres and Hallingdal in order to reinforce the main front in eastern Norway. The focus of the remaining forces in western Norway became the prevention of the Germans from advancing from the area round Bergen. Norwegian naval forces, organised into three regional commands by Kontreadmiral Carsten Tank-Nielsen, prevented German penetrations into the Hardangerfjord and Sognefjord. In total the Norwegian navy fielded some 17 or 18 warships and five to six aircraft in western Norway following the German capture of Bergen. After the Luftwaffe had bombed and severely damaged Voss and the area round it on 23/25 April, inflicting many civilian casualties, the Germans captured the town on 26 April.

After the Norwegian loss of Voss, Steffens evacuated what was left of his forces to the north, evacuating the southern side of the Sognefjord on 28 May but leaving a small contingent at Lærdal. Steffens established his headquarters at Førde and prepared for the further defence of Sogn og Fjordane. On 30 April a message from Ruge told of the evacuation of all Allied troops and also of the King Haakon VII and the army command, from southern Norway. With no support forthcoming from either Allied or Norwegian forces, on 1 May Steffens ordered his troops to disband. The advancing German forces were informed of the whereabouts of the Norwegian troops, and agreed to let them disband unmolested. On the night of 1/2 May, Steffens left for Tromsø with three naval aircraft, effectively ending the campaign in the region. No Allied land troops had been involved in the fighting in Hordaland and Sogn og Fjordane. Another two aircraft flew to the UK for continued service. Although the Norwegian navy’s ships in western Norway were ordered to evacuate to the UK or northern Norway, only the auxiliary patrol boat Bjerk sailed to the UK and Steinar to northern Norway. The remaining ships were either prevented from leaving by the desertion of many of their men, or had commanders who chose to dissolve their crews rather than risk the voyages to Allied-controlled territory. The last Norwegian forces in western Norway disbanded in Florø on 18 May 1940.

The original plan for the campaign in central Norway called for a three-pronged attack against Trondheim by Allied forces while the Norwegians contained the German forces to the south. This 'Hammer' was to land Major General A. Carton de Wiart’s 'Maurice' Force at Namsos to the north and Major General B. T. C. Paget’s 'Sickle' Force at Åndalsnes to the south, and around Trondheim itself Major General H. P. M. Berney-Ficklin’s 'Hammer' Force. This plan was quickly subjected to change as it was felt that a direct assault on Trondheim would be far too risky. so only the northern and southern landings were to be made.

In order to block the expected Allied landings, the Oberkommando der Wehrmacht ordered a Fallschirmjäger parachute company to make a combat drop on the railway junction of Dombås in the north of the Gudbrandsdal valley. This small force landed on 14 April and managed to block the rail and road network in central Norway for five days before being forced to surrender to the Norwegian Army on 19 April.

The leading element of the 'Sickle' Force arrived at Åndalsnes on 12 April. The landing of this force’s main strength, comprising Morgan’s British 148^th Brigade, took place on 17 April. The success of the Norwegian mobilisation in the area had opened the opportunity for the British landing.

In the late hours of 14 April, 'Maurice' Force, composed primarily of Brigadier G. C. Phillips’s British 146^th Brigade made its initial landing at Namsos. During its passage from the UK, the force had been transferred from unwieldy transport ships to destroyers as the waters of the fjord to Namsos were narrow. In the confusion of the transfer, however, a great part of the force’s supplies and even the brigade commander were misplaced. Another great problem for 'Maurice' Force was the lack of air support and effective anti-aircraft defences, something of which the Luftwaffe took full advantage. On 17 April the force moved forward from Namsos to positions around the village of Follafoss and the town of Steinkjer, and French troops started to arrive at Namsos late on 19 April. On 20 April German aircraft bombed Namsos, destroying most of the town centre’s buildings, as well as a major portion of the Allied troops' supply storage, leaving de Wiart without a base. Even so, he moved some 80 miles (130 km) inland to Steinkjer and linked with the Norwegian 5^th Division. Constant harassment from the air prevented any kind of offensive by the Allied troops, however, and on 21 April 'Maurice' Force came under attack by the 181^st Division from Trondheim. de Wiart was compelled by this attack to fall back, abandoning Steinkjer to the Germans. On 21 and 22 April Steinkjer was bombed by the Luftwaffe, leaving four-fifths of the town in ruins and more than 2,000 people homeless. By 24 April Steinkjer and the surrounding areas had been occupied by the Germans.

By 28 April, with both groups checked by the Germans, the Allied leadership decided to withdraw all British and French forces from the southern and central regions of Norway. Their retreat was covered by Norwegian forces, which were then demobilised so that the men would not become prisoners of the Germans. On 30 April the Germans advancing from Oslo and Trondheim met.

On 28 and 29 April the undefended port town of Kristiansund had been heavily bombed by the Luftwaffe, as was the nearby port of Molde, which functioned as the headquarters of the Norwegian government and the king. The town of Ålesund had also suffered heavily from German bombing during the last days of April.

'Sickle' Force managed to return to Åndalsnes and Molde, from which they were evacuated in 'Brick' and 'Tunnel' by 02.00 on 2 May, just a few hours before the 916^th Division[p/e] captured the ports. Åndalsnes had been subjected to heavy German bombing between 23 and 26 April, and had been burning until 27 April. The village of Veblungsnes and the area around Åndalsnes train station suffered particularly heavy damage. By the time the Germans arrived, some 80% of Åndalsnes lay in ruins. 'Maurice' Force, its convoys delayed by thick fog, was evacuated from Namsos in 'Klazon I' on 2 May, though two of is rescue ships, the French destroyer Bison and the British destroyer Afridi were sunk by Ju 87 dive-bombers.