the United Kingdom. On 14 December 1939, Raeder introduced Adolf Hitler to Vidkun Quisling, a pro-Nazi former defence minister of Norway. Quisling proposed pan-Germanic cooperation between Nazi Germany and Norway. In a second meeting on 18 December, Quisling and Hitler discussed the threat of an Allied invasion of Norway. After the first meeting with Quisling, Hitler ordered the Oberkommando der Wehrmacht (OKW) to begin investigating possible invasion plans of Norway. Meeting Quisling was central in igniting Hitler's interest in bringing the country effectively under his control. The first comprehensive German plan for the occupation of Norway, Studie Nord, ordered by Hitler on 14 December, was completed by 10 January 1940. On 27 January, Hitler ordered that a new plan, named Weserübung, be developed. Work on Weserübung began on 5 February. Altmark incident The Altmark incident occurred in the late hours of 16 February 1940 when the Royal Navy destroyer entered Norwegian territorial waters, intercepting and boarding the German auxiliary ship in the Jøssingfjord. Altmark had spent the prior months as a fleet oiler turned prison ship for the German cruiser while the latter was acting as a commerce raider in the South Atlantic. When she began the return journey to Germany, she carried 299 prisoners taken from Allied ships sunk by the Graf Spee. She rounded Scotland, then entered Norwegian territorial waters near the Trondheimsfjord, flying the Imperial Service Flag (Reichsdienstflagge). A Norwegian naval escort accompanied Altmark as she proceeded southwards, hugging the Norwegian coastline. As Altmark was nearing Bergen harbour on 14 February, the Norwegian naval authorities demanded an inspection of her cargo. International law did not ban the transfer of prisoners of war through neutral waters, and the German captain refused the inspection. This led the commander in Bergen, Admiral Carsten Tank-Nielsen, to deny Altmark access to the restricted-access harbour zone. Tank-Nielsen was overruled by his superior, Commanding Admiral Henry Diesen, and she was escorted through. Per Norwegian neutrality regulations, government ships operated by the warring countries were forbidden from such strategically important Norwegian ports. This violation of the regulations was because Diesen feared that the British would intercept Altmark if she was forced to sail further out. On 16 February, Altmark was spotted by three British aircraft. This led the Royal Navy to send one light cruiser and five destroyers that were patrolling nearby. Under the attack of two British destroyers (HMS Ivanhoe and Intrepid), Altmark fled