From 1944, the operative responsibility for Bærumbanen was taken over by Oslo Sporveier. The Lilleaker–Østensjø Line was then given the service number 9. The municipalities of Oslo and Aker merged in 1948, and the ownership of the Østensjø Line was transferred to Bærumsbanen. The remaining Class A trams were retired between 1946 and 1958 and replaced with Class E, very similar to Class B, but had been built as street trams in 1939. Class B trams were rebuilt from 1955 so they could operate in trains.