 On 5 December 1943, Line 21, from Carl Berners plass to Skillebekk, was opened as a trolleybus, with 11 buses being used on the route.From 1944, it was the only bus route being run by Oslo Sporveier.The same year, the Norwegian resistance blew up the garage at Bjølsen, which was being used to manufacture part to German Messerschmidt ME-109 aircraft.