Westfalen initially operated as a ferry for the shipping company Deutsche Lufthansa AG, Berlin until 1933 when it was converted into a service ship for military aircraft. The aircraft could take off from the deck and land on the water when they returned and were taken aboard with the help of a crane. In April 1941, Westfalen was converted into a troop transport ship and operated as a prisoner transport between Norway and Germany.

On 7 September 1944, Westfalen left Norway to go south towards Germany with 80 prisoners, 50 of whom were Norwegians and the rest were Germans. Some of them were to become slave laborers in Germany and some were to go to concentration camps. The prisoners were kept at the bottom of the ship. The head of the prisoner transport was SS Sturmscharfführer Wilhelm Heinze, a notorious Gestapo man in Kristiansand. There were also 200 Germans on board who were going on leave to Germany.

At 11:15 on 8 September, the ship was torpedoed just northwest of Hönö. First with a bang in the bow followed by a torpedo that hit the stern. At the explosions, the prisoners got on deck. Everyone on board tried to get into the lifeboats to escape the sinking ship.

The Swedish destroyer Karlskrona intercepted the distress signals from Westfalen and was quickly on the scene and was able to rescue 46 Germans who were in a lifeboat and from a raft four men were taken aboard while two others drowned while trying to haul them aboard. Another man who was alone on a raft was also rescued. The destroyer Göteborg and Klas Horn also participated, one of whom managed to save seven men from a raft. Fishermen and the pilot from Marstrand also participated in the rescue operation and the pilot took five men aboard.

At the time of the accident, the sea was rough and it was therefore difficult for the helping ships to take people on board. Of those rescued, 11 were taken to hospital in Gothenburg. By 11pm the Swedish Navy ship had rescued 66 people alive and 23 dead and the pilot boat had rescued nine people alive and five dead. Two Germans drifted ashore on Tjörn and they survived thanks to the fact that they were wearing life jackets. 15 minutes after the explosions the ship buckled and buckled and sank. Of the 200 Germans and 80 prisoners, only 78 men survived, of whom only five were prisoners.