because of the break-out of the Second World War. Construction resumed in April 1941 and later the same year the first Class C trains were put into service. The work also involved widening the profile between Jar and Egne hjem so the Class C could operate on the whole length of the line. The connection from Jar to Sørbyhaugen opened on 15 June 1942. Double track was installed from Haslum to Kolsås; this opened on 23 December. A further six Class C were delivered, matching loading gauge of Holmenkolbanen's lines. In addition, two Class A trams were converted to the wider and longer Class D. With the opening of the connection, the section from Sørbyhaugen to Kolsås was designated the Kolsås Line, and the section from Jar to Skøyen was designated as the Lilleaker Line. A balloon loop was built at Jar, allowing the new Class B trams that served the Lilleaker Line to turn there. This allowed for transfer between the two lines. The distance from Kolsås to Nationaltheatret was . During World War II, ridership on the whole tramway, including the Kolsås Line, skyrocketed. The line transported 5.7 million passengers in 1938, while in 1944 it transported 19 million. Ownership of rolling stock and all but two employees in Bærumsbanen were transferred to Oslo Sporveier in 1944. However, the ownership of the tracks and the formal operation rights remained with Bærumsbanen. Post-war operations By the end of the war in 1945 the line was in need of a major overhaul, in particular the overhead wires. Lack of materials and money caused the extraordinary maintenance to take four years. Limitations of freight were imposed in 1946, and were terminated the following year. At the same time, the Kolsås Line services were internally numbered 14, but it was first many years later that the number appeared on the destination signs and schedules. A former barracks was moved to Avløs in 1948, where it was used as office space. The line had unchanged fares from 1939 to 1951, when the prices hiked 27 percent. However, this was not sufficient to cover the 170 percent cost increase in the same period. From 1949 to 1966, Avløs Depot built nine new Class C trams. The line also received two Class T trams in 1963, which were prototypes for the first Oslo Metro rolling stock. Mærradalen was closed on 5 July 1957 and the