Battle of Drøbak Sound
The Battle of Drøbak Sound took place in Drøbak Sound, the northernmost part of the outer Oslofjord in south-eastern Norway, on 9 April 1940. It marked the end of the "Phoney War" and the beginning of World War II in Western Europe.
A German fleet led by the cruiser Blücher was dispatched up the Oslofjord to begin the German invasion of Norway, to seize the Norwegian capital of Oslo and capture King Haakon VII and his government. The fleet was engaged in the fjord by Oscarsborg Fortress, an aging coastal installation near Drøbak, that had been relegated to training coastal artillery servicemen, leading the Germans to disregard its defensive value. However, unbeknownst to German military intelligence, the fortress' most powerful weapon was a torpedo battery, which would be used to great effect against the German invaders.
The fortress' armaments worked flawlessly despite their age, sinking the Blücher in the sound and forcing the German fleet to fall back. The loss of the German flagship, which carried most of the troops and Gestapo agents intended to occupy Oslo, delayed the German occupation long enough for King Haakon VII and his government to escape from the capital.
Before the battle
Norway
Oscarsborg Fortress was commanded by 64-year-old Oberst Birger Eriksen. He had not received clear orders and no information on whether the approaching warships were German or Allied. He knew that Norway was officially neutral but that the government was inclined to side with the British if Norway became a belligerent.The fortress' main command station and battery were on Håøya island north-west of South Kaholmen Due to the unique circumstances in 1940, Eriksen commanded from the backup station at South Kaholmen, east of the main battery.
Apart from the officers and NCOs, most of the remaining garrison consisted of 450 fresh troops conscripted on 2 April. The naval mines were not deployed; deployment was scheduled for a few days after 9 April as a recruit training exercise.
The main battery consisted of three 28 cm MRK L/35| Krupp guns called Moses, Aron and Josva. There were enough trained gunners for one gun. They were split between two guns and assisted by non-combatant privates, including cooks. All the guns were loaded with live high-explosive shells.
The fortress' torpedo battery was armed with 40-year-old Austro-Hungarian Whitehead torpedoes. The weapons had been practice-launched over 200 times; despite doubts they functioned properly during the battle. The battery had three launch tunnels opening below the surface. There were six torpedoes ready to launch, and another three as reloads.
The torpedo battery was commanded by Kommandørkaptein , who lived in Drøbak. He was a temporary substitute for the commanding officer who went on sick leave in March 1940. Late on 8 April, during the action in the Oslofjord, Eriksen ordered Anderssen to the battery; Anderssen donned his old uniform and was transported across the fjord to the battery by boat. Anderssen was familiar with the post; he first served at the battery in 1909 and was its commander by the time he retired in 1927. Anderssen was recalled to active duty in March.
Germany
The objective of the German naval force was to capture the Norwegian capital, Oslo, King Haakon VII, and the Norwegian government. It was led by the cruiser Blücher, a new warship with an inexperienced crew. Those onboard included Generalmajor Erwin Engelbrecht, Admiral Oskar Kummetz and a special unit for capturing the king.The Germans underestimated the operational value of the Norwegian coastal fortifications; the fortifications were old and used for training. The Germans did not know of the Oscarsborg torpedo battery.
Battle
The main battery fires
At 4:21 a.m. on 9 April, Eriksen ordered the main battery to fire on Blücher, the lead ship of the German flotilla heading to Oslo. When his order was questioned, Eriksen replied: "Either I will be decorated or I will be court-martialled. Fire!" Firing without warning shots violated the pre-war Norwegian rules of engagement. The German ships had already received warning and live shots from outlying fortifications; Eriksen later used this to justify his decision to consider the ships to be hostile.Two guns, Moses and Aron, each fired one high-explosive shell. The first shell struck the front of the mainmast and set the midship area up to the fore mast on fire; this detonated a magazine containing stores for the Arado Ar 196 reconnaissance floatplanes – oil cans, smoke dispensers, incendiary bombs, aircraft bombs and depth charges. Shortly after the first hit, the second shell hit the base of one of the forward gun turrets, throwing debris from it overboard and igniting further fires; this put the ship's main guns out of action by disabling their electrical power. The unmanned third gun, Josva, was not fired. No further shells were fired; the guns could not be reloaded in time with the untrained gunners.
The secondary batteries fire
Next, the secondary Norwegian coastal batteries opened fire on Blücher. The weapons ranged from two small guns 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 57 mm guns targeted the cruiser's superstructure and anti-aircraft weapons, and partially suppressed German return fire. Blücher continued to sail slowly northward. It passed close enough to fire on the Husvik battery with light AA guns. The Norwegians abandoned Husvik; its main building caught fire but there were no casualties. In all, the cruiser was hit by thirteen 15 cm and around thirty 57 mm shells. One 15 cm hit from Kopås disabled the steering gear; the ship avoided grounding by steering with its engines. Shell fragments disabled the firefighting system.The fortress' gun batteries had been in action for only five to seven minutes. Return fire from Blüchers light battery was ineffective due to excessive elevation.
At this point, Germans voices on the cruiser became audible to the Norwegians, alerting the latter of their opponent's identity; according to the Norwegians, the Germans began to sing Deutschlandlied, the German national anthem. The Norwegian minesweeper HNoMS Otra had identified the intruders as Germans earlier and communicated this to the Horten naval base at 04:10. Norwegian communications problems delayed its delivery to Oscarsborg; Eriksen received it at 04:35. There was then "a dead silence on board the whole ship, no movement whatsoever was identified".
The torpedo battery fires
Blücher was crippled but remained afloat. It continued to move north, which brought it within of Oscarsborg's torpedo battery. Anderssen fired the first torpedo at about 04:30. The target's speed was slightly overestimated, and the torpedo struck near the ship's forward turret and caused inconsequential damage. The aim was corrected for the second torpedo; it struck amidship in the same area as the first 28 cm shell hit. The hit disabled the engines, blew open bulkheads and caused flooding. The ship continued to burn.The fortress' third torpedo tube was not fired in case of further targets. The other tubes were reloaded.
''Blücher'' sinks
Blücher anchored near the Askholmene islets just north and out of the field of fire of the fort's guns. The crew attempted to fight the uncontrolled fires. Torpedoes were fired to prevent their detonation by the fires. At 05:30, the fires detonated a midship magazine for the Flak guns, blowing a hole in the ship's side ruptured the bulkheads between the boiler rooms, and caused further fires by opening fuel tanks.Blücher sank bow-first at 06:22, capsizing to port. Two thousand German sailors and soldiers were in the freezing water. Hundreds died when floating fuel oil caught fire.
Approximately 1,400 Germans survived and 650–800 died. 1,200 came ashore at Frogn near Drøbak. 550 were captured by His Majesty the King's Guard, 4th Company, commanded by Kaptein A. J. T. Petersson. The guardsmen were supposed to take all the Germans prisoner, but mainly focused on treating casualties. Around 1,000 Germans, including Engelbrecht and Kummetz, were eventually moved to a nearby farm and placed under light guard. The prisoners were not interrogated, and were effectively freed when the Norwegians withdrew by 18:30. Engelbrecht and Kummetz reached Oslo at 22:00, establishing themselves in the Hotel Continental, and occupying the capital with their remaining troops. Norwegian wounded and many German wounded were treated by the Royal Norwegian Navy Hospital at the Asgården summer hotel in Åsgårdstrand; the hospital had been evacuated from Horten at midnight on 8 April.
Remaining ships retreat
When Blücher was hit by the torpedoes, the commander of the heavy cruiser Lützow – unaware of the torpedo battery – assumed the presence of mines. At 4 h 40, the Germans decided to withdraw and land their troops out of range of the Oscarsborg guns. The attack on Oslo would continue by a landward advance up the Oslofjord.The retreating Lützow was hit by three 15 cm shells from the Kopås battery, which disabled the cruiser's forward 28 cm turret. Kopås continued to fire until the German ships disappeared into the mist at a range of around. Lützows aft turret bombarded the Norwegians from a range of down the fjord.
The first Norwegian civilian ship lost during the invasion, the Norwegian cargo cutter, was sunk during the battle. Sørland was carrying paper from Moss to Oslo when it stumbled into the battle, which it thought was an exercise. It was attacked and set on fire by the German minesweepers R-18 and R-19 and sank near Skiphelle in Drøbak with the loss of two of its six crew. The burning ship was misidentified by the Norwegians as the German training ship. The real Brummer was lost in connection with the invasion. It was torpedoed on 14 April by the Royal Navy submarine while returning to Germany and sank the next day.