Battle of Drøbak Sound The Battle of Drøbak Sound took place in the northernmost part of the Oslofjord on 9 April 1940 , on the first day of the German invasion of Norway . It was the start of the war in Western Europe — and an end to the " Phoney War " . Oscarsborg Fortress near Drøbak engaged a German fleet sailing up the Oslofjord with the objective of seizing the Norwegian capital and capturing Haakon VII , the Norwegian king , and his government . At the time of the battle , the ageing fortress ' Main Battery of guns was over 40 years old and the installation had been relegated to training coastal artillery servicemen , leading the Germans to disregard the fortress ' defensive value . Furthermore , the most powerful weapon of the fortress was a torpedo battery , which no one but the Norwegian military knew about . In the end , the fortress ' armament worked flawlessly . By sinking the lead ship of the German armada headed for Oslo , Oscarsborg Fortress saved the Norwegian king and government from being taken captive in the first hours of the invasion . Before the Battle . As the political situation was chaotic , the ageing 64 - year - old commander , " Oberst " ( Colonel ) Birger Eriksen had not received any clear orders and had received no notice as to whether the approaching warships were German or Allied . He was well aware that Norway was officially neutral , but that the government was inclined to side with the British in case of direct Norwegian involvement in the war . As he was about to give orders to fire , Eriksen said : " Either I will be decorated , or I will be court - martialed . Fire ! " Apart from the officers and NCOs , almost all soldiers manning the fortress were fresh recruits , having only been conscripted seven days before , on 2 April . Because of the influx of 450 fresh recruits , the fortress ' naval mine s were not deployed on 9 April . Part of the recruits ' training was to lay the mine barrier , a process planned for a few days later . The torpedo battery . The commander of the torpedo battery at Oscarsborg had at the time of the battle been on sick leave since March 1940 . Due to this , the retired " Kommandørkaptein " ( Commander Senior Grade ) Andreas Anderssen , who lived in nearby Drøbak , had been assigned as temporary commander for the battery . As an unidentified flotilla started forcing its way past the outer fortifications in the south of the Oslofjord , late at night on 8 April , " Oberst " Eriksen called Anderssen in and had him come down to the fortress . " Kommandørkaptein " Anderssen donned his old uniform and was transported by boat over the fjord to the torpedo battery . Anderssen would show himself worthy of the important task of leading the fortress ' most lethal weapon system ; having first served at the torpedo battery in 1909 , he knew the ageing weapons intimately . When Anderssen had been called back into duty a month previously , he had been a pensioner for 13 years , having originally retired from his post as commander of the torpedo battery in 1927 . The battery had three torpedo tunnels which could fire six torpedoes without reloading and a total of nine torpedoes were stored and ready for use . The battle . The Main Battery rounds . While the main combat station for the Main Battery and the commander of Oscarsborg fortress was on the island Håøya north - west of South Kaholmen , due to the special circumstances in 1940 , " Oberst " Eriksen took position in the backup station on the eastern flank of the main battery at South Kaholmen . At 04 : 21 on 9 April , Eriksen gave the Main Battery guns the order to fire at the lead ship of the unknown flotilla forcing its way towards Oslo . Upon giving the command , Eriksen was questioned . He responded with his now famous response ; " Either I will be decorated or I will be court martialled , Fire ! " Two rounds from the Krupp guns " Moses " and " Aron " engaged the German cruiser at range . The two Norwegian guns had been loaded with live , high - explosive shells ; firing them " in anger " was a violation of the pre - war Norwegian rules of engagement which dictated warning shot s be fired first , as had been the case at Oslofjord Fortress further down the fjord . Colonel Eriksen later explained his decision by alluding to the fact that the German naval force already had forced their way past the Oslofjord Fortress ' forts and had received both warning shots and live rounds from these more outlying coastal fortifications . As the vessels had continued up the fjord toward the capital , Eriksen was of the opinion that he had the right to consider them enemy warships and to engage them as such . The first 28 cm shell hit " Blücher " right in front of the aft mast , and set the midship area up to the fore mast on fire . The second 28 cm round hit the base of the forward gun turret shortly thereafter , throwing large parts of it into the fjord and igniting further fires on board . There was only time for the Main Battery to fire these two rounds , due to their slow reload time with only 30 untrained recruits manning them at the time . Only one gun crew of actual artillerymen was available , and two guns could only be made operational by splitting the real gunners between the two guns and using non - combatant privates to assist the gunners . The personnel pressed into service on the main guns included cooks woken up to man the Main Battery . There was no time to reload ; there was not even time to fire the third gun , " Josva " , which was loaded but unmanned . The reason for the significant effect of the two 28 cm rounds on " Blücher " was that the first round penetrated the side of the ship and exploded inside a magazine containing cans of oil , smoke dispensers , incendiary bombs , aircraft bombs for the cruiser ' s Arado Ar 196 reconnaissance floatplane s and depth charges . The bulkheads on that deck were blown out and the burning oil developed into an intense fire . The second 28 cm shell also knocked out the electricity central for the ship ' s main guns , rendering them unable to return fire . The Kopås and Husvik batteries . While fire raged aboard " Blücher " , the secondary Norwegian coastal batteries pelted her with guns ranging in calibre from the two small pieces at Husvik , intended to protect the fortress ' missing mine barrier , to the three guns of the Kopås Battery on the eastern side of the fjord . The larger guns wrought havoc on board " Blücher " , while the 57 mm guns concentrated on the cruiser ' s superstructure and the anti - aircraft weapons , and were partially successful in suppressing the fire from her light artillery as " Blücher " slowly sailed past the fortress . The Husvik battery had to be abandoned when " Blücher " passed in front of it and fired her light AA guns directly down into the positions . Although the main building at the battery caught fire , the Norwegians suffered no casualties . In all , thirteen 15 cm rounds and around thirty 57 mm shells hit the German cruiser as it passed the guns of the fortress ' secondary batteries . One of the 15 cm rounds from Kopås disabled " Blücher " s steering gear and forced the cruiser ' s crew to steer her using the engines and propeller to avoid running aground . " Blücher " s fire - fighting system was also knocked out by shell fragments from the two Norwegian batteries , making attempts to control the fires aboard the ship and rescue the many wounded much more difficult . The identity of the intruders becomes known . As the now crippled " Blücher " passed the fortress guns , a sudden outburst of voices from the burning cruiser could be heard above the battle noises ; Norwegian sources state that the crew broke into singing " Deutschland , Deutschland über alles " . Only at this point did it become clear to the men of the fortress whom they were fighting . Later , at 04 : 35 , " Oberst " Eriksen received a message from the Norwegian minesweeper HNoMS " Otra " confirming that the intruding ships were German . The message had been sent to the naval base in Horten at 04 : 10 , but the massive communications problems that severely hampered the efforts of the Norwegian military throughout the Norwegian Campaign had prevented it from reaching Oscarsborg in time . The return fire from " Blücher " was ineffective , with the light artillery mostly pointing too high and the main batteries , 20 . 3 cm guns , unable to fire due the damage caused by the second 28 cm round from Oscarsborg ' s Main Battery . The shelling lasted only for five to seven minutes . When the guns on both sides silenced , with all the " passengers " still under deck — " there was a dead silence on board the whole ship , no movement whatsoever was identified " . " Kommandørkaptein " Anderssen launches the torpedoes . After passing the line of fire of the fortress ' gun batteries , the cruiser was burning and severely damaged , but her captain still hoped he would be able to save his ship . At this point , however , " Blücher " entered the sights of " Kommandørkaptein " Anderssen as she slid past the torpedo battery at a range of only . The torpedoes the retired officer was aiming at the cruiser were 40 - year - old Whitehead weapons of Austro - Hungarian manufacture . These torpedoes had been practice - launched well over 200 times before , but no one was certain if they would function or not . As " Kommandørkaptein " Anderssen pushed the firing mechanism , at approximately 04 : 30 , the weapons turned out to work perfectly , first one and then another torpedo raced out of their underwater exit tunnels at below the surface toward the burning warship . As Anderssen had overestimated the speed of his target slightly the first torpedo hit near " Blücher " s forward turret ( nicknamed " " Anton " " ) , creating only inconsequential damage . With the second torpedo launch the aim was corrected and the torpedo struck " Blücher " amidships , hitting the same general area as the first 28 cm shell . This caused catastrophic damage to the cruiser and blew open many of her bulkheads , allowing water to flood her decks while she was burning furiously . The third torpedo launcher was left loaded in case more ships were to follow close behind " Blücher " . After firing , the two other tubes were reloaded and readied for the next target . End of the " Blücher " . With all engines knocked out by the second torpedo hit , the cruiser anchored near the Askholmene islets just north and out of the arc of fire of the fort ' s guns to try to fight the ferocious fires raging throughout the vessel . " Blücher " s torpedoes were fired against land to avoid them exploding in the uncontrolled fires aboard . The crew ' s struggle ended when , at 05 : 30 , fires reached a midship ammunition hold for the " Flak " gun s , blowing a huge gap in the ship ' s side . The magazine blast ruptured the bulkheads between the boiler rooms and tore open the cruiser ' s fuel bunkers ; igniting further fires . By this point , " Blücher " was doomed . At 06 : 22 , " Blücher " sank bow first into the depths of the Oslofjord , first laying over on her port side , then turning upside - down and finally succumbing with her screws the last to disappear below the surface . After the ship had disappeared from the surface , large quantities of oil floated up and covered the close to two thousand sailors and soldiers fighting for their lives in the freezing water . The oil rapidly caught fire , killing further hundreds of Germans . " Obergefreiter " Günther Morgalla — who survived the sinking — later told that , swimming toward his shivering crew mates onshore , he had heard someone singing in obstinacy to this fate , the " Deutschlandlied " followed by " " Das kann doch einen Seemann nicht erschüttern . " " ( " " That cannot shake a sailor " " ) . In all , some 650 - 800 Germans died , and some 550 of the around 1 , 400 wet and cold survivors of " Blücher " were captured , by soldiers from Company no . 4 of the Norwegian Royal Guards under the command of " Kaptein " ( Captain ) A . J . T . Petersson . In total , some 1 , 200 of the survivors had made it ashore at Frogn near Drøbak and the guardsmen were supposed to take all these as prisoners , but instead focused on tending for the many wounded and dying . By doing this , the Norwegians neglected their original orders and allowed for the German top officers , chief amongst whom was " Generalmajor " Erwin Engelbrecht , to slip away to the nearest road and capture a Norwegian truck at gunpoint . The German leading officers reached the Hotel Continental in Oslo only two hours later than planned , though without the troops intended to occupy the Norwegian capital . Many of the German wounded were initially taken to Åsgården summer hotel in Åsgårdstrand for medical care , where Norwegian wounded had already been brought . The hotel was the temporary improvised location for the Royal Norwegian Navy Hospital , which had been evacuated from Horten at midnight on 8 April . The remaining ships turn around . By the time " Blücher " sank , the remaining naval force destined for Oslo had long since turned around and retreated back down the fjord . Seeing the geysers of water from underwater explosions on " Blücher " , and unaware of the torpedo battery , the commander of the heavy cruiser " Lützow " assumed the flagship had hit mines and at 04 : 40 the decision was made for the flotila to turn back and land the invasion forces out of range of the Oscarsborg batteries . The planned coup against Oslo to force the surrender of the Norwegian government was replaced by a land advance up the Oslofjord . As the force made good its escape , the fortress managed to damage " Lützow " , the 15 cm guns of the Kopås battery scoring three hits and knocking out the ship ' s aft 28 cm turret ( " Bruno " ) . Kopås kept firing at the retreating ships until they disappeared in the mist at a range of around . After pulling out of range of the fortress guns , " Lützow " employed her remaining turret " Anton " to bombard the defenders from a range of down the fjord . During the battle , another burning ship was spotted in the distance from Oscarsborg , leading the Norwegian defenders to believe they had sunk one more German warship in addition to " Blücher " . For some time after the battle , the belief was that Oscarsborg had sunk the artillery training ship . The reality , however , was that the burning ship was the Norwegian cargo cutter " Sørland " that had stumbled into the battle while on her way from Moss to Oslo with a cargo of paper . As the small ship had mistaken the events as a military exercise , she kept going until fired upon and set ablaze by the German minesweepers " R - 18 " and " R - 19 " . " Sørland " sank with two of her six - man crew near the village of Skiphelle in Drøbak , as the first civilian Norwegian ship lost during the invasion . " Brummer " was indeed lost in connection with the invasion , but only when she was on her way back to Germany on 14 April , when she was torpedoed by the Royal Navy submarine and sank the next day . " Luftwaffe " bombing . The fortress was subjected to heavy " Luftwaffe " bombing later on the same day , to which the fortress could only reply with two Bofors 40 mm L / 60 anti - aircraft ( AA ) gun s and three Colt M / 29 AA machine gun s at Seiersten Battery , as well as another four Colt M / 29 7 . 92 mm AA machine guns at Håøya Battery , but again without Norwegian casualties . Initially , four machine guns on the roof of the Main Battery also returned fire , but these had to be abandoned early on in the bombing . One of the two 40 mm anti - aircraft guns became unserviceable after only 22 rounds ; the other gun kept firing until 12 : 00 , but to little effect . After a break in the attacks from 12 : 00 - 13 : 30 , during which time " Lützow " bombarded Hovedøya , the " Luftwaffe " bombers returned at 13 : 30 and soon strafed the remaining Norwegian anti - aircraft guns , forcing the crew to seek shelter in the nearby forest at around 14 : 00 . In all , the fortress was subjected to close to nine hours of air attack , during which time around 500 bombs — ranging from in size — were dropped on Oscarsborg . Surrender . Although the German naval attack on Oslo had been thwarted by the actions of Oscarsborg , the city was seized later that day by forces that were airlifted into Fornebu Airport . In light of the capture of the capital , and with news of German landings at the village of Son south of Drøbak , Colonel Eriksen decided that further fighting without adequate infantry support was in vain . The fortress was surrendered intact on the morning of 10 April . Aftermath . In one of the more peculiar battles of the war , a hundred year old fortification , manned by recruits and pensioners and armed with 40 - 50 year old weaponry of German and Austro - Hungarian manufacture had destroyed a ship so new , its crew was still finishing training . Oscarsborg had fulfilled its mission and denied an invader the way to the capital . Even though it and the country ultimately were captured and occupied , the effects of delaying the German advance were immediate and considerable . On board " Blücher " were troops specially designated to capture the King , the Norwegian cabinet , the Storting ( Norwegian Parliament ) and the national gold reserve ; the delay made it possible for all these to escape from Oslo . Later in the day of 9 April , the Storting was able to convene at Elverum and give the cabinet a wide authorization to govern until a Storting could again assemble . Thus , the Norwegian government was able to continue the defence of Norway until it had evacuated to exile in the United Kingdom on 7 June , with the Norwegian Army laying down their arms on 10 June .