population about 24,700
During the Winter War, Oulu had several air raid warnings, but the city was only bombed twice by Soviet planes, on 1 and 21 January 1940. The bombings claimed the lives of five people. The estimated material damages caused by the firebombs of the second bombing exceeded three million Finnish marks.
population about 27,000
In the Continuation War, the front was far from Oulu. Various Finnish and German training and service centres and headquarters were located in Oulu. Oulu was a German garrison town, and the Germans had established a local commandant's office at Seurahuone. The town was still run by Finnish military and civil authorities – the rights of the Germans were limited to German issues.
At one point there were over 4,000 Germans in Oulu, and solders passing through the town accentuated the amount of Germans. There were both Finnish and German war hospitals in Oulu, and soldiers from the front came to Oulu for their leave.
The name of the Alppila (Alps) district dates back to the German period. The building where the Alppila fire station is now based was originally a German officers' mess.
The Soviet air bombings in February 1944 caused the greatest amount of damage. Four people died and material damages were estimated to exceed 100 million Finnish marks.
When Finland and the Soviet Union declared a truce on 19 September 1944, the Germans left Oulu peacefully. However, Lapland faced the Lapland War, which lasted until April 1945. During the war, the Germans left Lapland devastated.
population about 35,540
Electricity production at the Merikoski hydroelectric power plant began in 1948 when the first generator was started. The city-owned plant had been built partly during the war. Some of the construction work during the war was carried out by Soviet prisoners of war who were held in a prison camp in Oulu. During the busiest construction years, about half of the city budget was spent on the plant.
Evacuees from the areas surrendered to the Soviet Union were the biggest group of newcomers in Oulu. At the end of 1948, more than 1,100 evacuees resided in Oulu.
population about 39,900
The Typpi Oy factories in Laanila produced the first batches of ammonia, nitric acid and fertilizer. The buildings were designed by the Alvar Aalto architectural practice. Following various mergers and company name changes, the area now accommodates the Oulu works of the chemical industry company, Kemira Oy.
population about 51,500
The University of Oulu began operating in temporary premises in different parts of the city. The university had a crucial role in the development of Oulu. It facilitated industry and population growth and helped to create service industry jobs. Today (in 2021), the University of Oulu has eight faculties and is located in Linnanmaa and Kontinkangas.