During the night of 9 April, "Draug" was patrolling and watching shipping in the Karmsund. At about 02:00, Horve was notified that Oslofjord Fortress was engaging an unknown enemy force in the Oslofjord, leading to the crew being ordered to full combat stations. At 04:00, an unknown ship, flying no national flag, was observed sailing northwards through the Karmsund. The ship refused to stop after both flares and warning shots had been fired and "Draug" had to give chase and capture the vessel. After leading the unknown ship into Haugesund, its identity was found to be the 7,624 ton German vessel , with papers claiming she was carrying a cargo of 7,000 tons of coke to Bergen. When "Draug"s second-in-command, Lieutenant Østervold, tried to inspect the cargo, however, he was refused by the German captain, all entrances to the cargo hold also being blocked off to make a proper search impossible. In response, the inspecting officer decided to take the ship under arrest and sealed the radio room. The cargo hidden on board "Main" later turned out to have consisted of provisions and matériel for the invading German forces at Trondheim, chiefly some 2,000 naval mines