After the war new trains were purchased to run on the Metropolitan, District, Bakerloo and Piccadilly lines, the Piccadilly line trains having air-operated sliding doors. In the 1920s, taking advantage of government backed financial guarantees for capital projects that promoted employment, there were major extensions of the City & South London and the Hampstead lines. The tunnels of the City & South London Railway were rebuilt to have the same diameter of the other tubes, and the extended north from Euston to a junction with the Hampstead line at Camden Town, and south to Morden. The Hampstead line was extended to the north from Golders Green to Edgware and south to another junction with the City & South London at Kennington, this opening in 1926. Although physically connected, the lines were still officially named the City Railway and Hampstead & Highgate line. The lines were to be known as the Edgware, Highgate and Morden and the Morden-Edgware until finally renamed the Northern line in 1937. Also during the 1920s the original tube gate stock was replaced with 1,460 cars of Standard Stock with air-operating sliding doors, except for the Central line where the cars were refurbished. Busy central London stations were modernised with escalators replacing lifts.