The Allies assumed that Wilfred would provoke German retaliation in Norway and prepared Plan R4 to occupy Narvik, Stavanger, Bergen and Trondheim.

The deputy permanent under-secretary at the Foreign Office, Orme Sargent, wrote ...our desire to assist Finland is only a pretext to justify our occupying Northern Sweden.

The War Cabinet and the Ministry of Economic Warfare hesitated to support hostilities in Norwegian waters, because of the effect that they could have on British imports from Norway and Sweden.

In Operation Avonmouth, three battalions of Chasseurs Alpins and a British infantry brigade, with three ski companies attached, were to land at Narvik and advance along the railway to take over the iron ore fields in Lapland.

The French chasseurs and Foreign Legionnaires were to continue east towards Finland but keep away from the Red Army and risk being cut off by a German force when the ice in the Gulf of Bothnia thawed.

The British commanders were briefed on 12 March that they were to land a force at Narvik, assist Finland and deny Russia and Germany the Swedish iron ore fields for as long as they could.

[9] By late March 1940, after the resignation of Daladier and the appointment of Paul Reynaud as prime minister of France, at the Supreme War Council, Chamberlain presented Operation Royal Marine, a scheme to put floating mines into the Rhine to disrupt river traffic downriver in the Rhineland.

[10] On 3 April, the British began to receive reports of an accumulation of shipping and troops in the Baltic German ports of Rostock, Stettin and Swinemunde.

Force WB, with two destroyers, was to lay a dummy minefield off the Bud headland, south of Kristiansund (62°54'N, 6°55'E) if the Norwegians swept the mines, they were to be replaced by the minelayers.

Brigadier C. G. Phillips and two battalions of infantry for Bergen and two for Stavanger embarked at Rosyth on 7 April in the cruisers HMS Berwick, York, Devonshire and Glasgow.

[12] On 3 April, the cruisers Berwick, York, Devonshire and Glasgow with the destroyers HMS Afridi, Cossack, Gurkha, Mohawk, Sikh and Zulu embarked their troops at Rosyth to be transported to Norway for Plan R4.

[13] As Force WS sailed for Stadtlandet on 7 April, German ships were sighted in the Heligoland Bight on passage to Norway and the mine laying was cancelled.

Soon afterwards, Force WB simulated mine laying off the Bud headland by using oil drums and patrolled the area to "warn" shipping of the danger.

[citation needed] Later that day, the ore carrier Rio de Janeiro, sailing from Stettin, in northern Germany was sunk in the Skagerrak by the Polish submarine Orzeł.

Around half of the 300 men on board were drowned, survivors telling the crews of the Norwegian fishing boats that picked them up that they were on their way to Bergen to defend it from the British.

[citation needed] HMS Glowworm (Lieutenant-Commander Gerard Roope), had become detached from the main force on 6 April to look for a man lost overboard and encountered the German heavy cruiser Admiral Hipper.

Glowworm carried out a torpedo attack and after receiving return fire and suffering severe damage, she rammed Admiral Hipper, sinking soon afterwards, with the loss 111 men; Roope was awarded a posthumous Victoria Cross.

[15] Renown, which had diverted to assist Glowworm, fought the Action off Lofoten with the German battleships Scharnhorst and Gneisenau 80 nmi (150 km; 92 mi) off the coast.