and the artillery training ship Bremse were damaged, the former seriously. The lack of working lights reduced the effectiveness of the guns though, and the landing ships were able to dock without much opposition. The fortifications were surrendered soon after, when Luftwaffe units arrived. The fortifications at Kristiansand put up an even more resolute fight, twice repulsing the landing and damaging , nearly causing her to run aground. Confusion soon sprung up though, when the Norwegians received the order not to fire on British and French ships and the Germans began to use Norwegian codes that they had captured at Horten. The Germans also used this opportunity to quickly reach the harbour and unload their troops, capturing the town by 11:00. While most of Gruppe 4 was engaged at Kristiansand, the torpedo boat captured Arendal without any opposition. The main objective at Arendal was the undersea telegraph cable to the United Kingdom. Gruppe 5 encountered the most serious resistance at the inner defensive fortifications of the Oslofjord, in the vicinity of Drøbak. , leading the group, approached the forts assuming that they would be taken by surprise and not respond in time, as had been the case with those in the outer fjord. It was not until the cruiser was at point-blank range that Oscarsborg Fortress opened fire, hitting with every shell. Within a matter of minutes, Blücher was crippled and burning heavily. The damaged cruiser was sunk by a salvo of antiquated, 40-year-old torpedoes launched from land-based torpedo tubes. She carried much of the administrative personnel intended both for the occupation of Norway and also for the headquarters of the army division assigned to seize Oslo. The cruiser , also damaged in the attack and believing Blücher had entered a minefield, withdrew with Gruppe 5, 19 km (12 mi) south to Sonsbukten where she unloaded her troops. This distance delayed the arrival of the main German invasion force for Oslo by over 24 hours, though the Norwegian capital would still be captured less than 12 hours after the loss of Blücher by troops flown into Fornebu Airport near the city. The delay induced by the Norwegian forces gave time for the royal family, Parliament, and with them the national treasury, to flee the capital and continue the fighting against the invasion force. Fornebu Airport was originally supposed to be secured by paratroops an hour before the first troops were