held by the Germans and to avoid damaging populated areas. The two met on 15 April to determine the best course of action. Lord Cork argued for an immediate assault on Narvik and Mackesy countered that such a move would lead to heavy casualties for his attacking troops. Cork eventually conceded to Mackesy's viewpoint. Mackesy's force was originally codenamed Avonforce, later Rupertforce. The force consisted of the 24th Guards Brigade, led by Brigadier William Fraser, and French and Polish units led by Brigadier Antoine Béthouart. The main force began landing at Harstad, a port town on the island of Hinnøya, on 14 April. The first German air attacks on Harstad began on 16 April, but anti-aircraft defences prevented serious damage until a raid on 20 May destroyed oil tanks and civilian houses and another raid on 23 May hit Allied shipping in the harbour. On 15 April, the Allies scored a significant victory when the Royal Navy destroyers and , which were escorting the troop-carrying Convoy NP1, forced the German U-boat to surface and scuttle in the Vågsfjorden. Found floating around the sinking U-boat were documents detailing the dispositions, codes and operational orders of all U-boats in the Norwegian operational area, providing the Allies with an efficient and valuable tool when planning troop and supply convoys to the campaign in northern Norway. After the Allied failure in Central Norway, more preparation was given to the northern forces. Air cover was provided by two squadrons of carrier-transported fighters operating from Bardufoss Air Station, the re-equipped No. 263 Squadron RAF with Gloster Gladiators and No. 46 Squadron RAF with Hawker Hurricanes. As part of the Allied counter-offensive in northern Norway, French forces made an amphibious landing at Bjerkvik on 13 May. The naval gunfire from supporting Allied warships destroyed most of the village and killed 14 civilians before the Germans were dislodged from Bjerkvik. While the Norwegian and Allied forces were advancing at Narvik, German forces were moving swiftly northwards through Nordland to relieve Dietl's besieged troops. The captured Værnes Air Station near Trondheim was rapidly expanded and improved to provide the Luftwaffe with a base from which to support the Narvik sector. As the German forces moved northwards, they also gained control of the basic facilities at Hattfjelldal Airfield to support their bomber operations. In late April, ten Independent Companies had been formed in Britain, commanded by Lieutenant Colonel Colin Gubbins.