London Underground 1906 Stock (Gate Stock)

These trains were built in the early twentieth century for the "Yerkes" tube lines which later became the Bakerloo, Northern and Piccadilly Lines. The 1906 Tube Stock as they became known had gateman operated lattice gates instead of air powered sliding doors (though some were later refitted with air doors later on) and were known as Gate Stock.
Approaching Hamstead Cross-over [1]

Information
Number built: 476 (168 Driving Motors, 86 Driving Trailers, 222 Trailers)
Built: 1906
Builder: American Car and Foundry, Les Ateliers de Construction
du Nord de la France, Hungarian Railway Carriage and
Machinery Works, Metropolitan Carriage & Wagon
Company, Brush Traction
Motor: 2 British Thomson-Houston electric motors per motor car
Power: 400 hp (298 kW) per motor car

The cars came from a variety of manufacturers. The Baker Street & Waterloo Railway (later Bakerloo Line) received one hundred and eight cars from the American Car and Foundry Company with final assembly at Trafford Park in Manchester [3]. The Bakerloo fleet was split in thirty six Driving Motors, Driving Trailers and Trailers each.

The Charing Cross, Hamstead and Euston Railway (later Northern Line) received one hundred and fifty cars from the American Car and Foundry Company. Their fleet consisted of sixty Driving Motors, fifty Driving Trailers and forty Trailers [4].
Motor car at Goldens Green [2]

The Great Northern, Piccadilly and Brompton Railway (later Piccadilly Line) received two hundred and eighteen cars. These were built mostly by Les Ateliers de Construction du Nord de la France and and the Hungarian Railway Carriage and Machinery Works with a couple of trailers also built by the Metropolitan Railway Carriage & Wagon Company and Brush Traction though these were too large to fit in the tunnels! [5] The Piccadilly fleet was split into seventy two motor cars and one hundred and forty six trailers.

All motor cars were fitted with British Thomson-Houston electrical equipment [6]. As mentioned above the 1906 Tube Stock had manually operated gates instead of sliding doors. This greatly increased the number of staff required on a train as each gate required a gateman. Typically a train might be crewed by a driver, guard and four gatemen. The Underground began to introduce sliding doors in the early 1920s [7] and the Gate Stock was quickly replaced by more modern trains, a small number of French built Driving Motors were fitted with sliding doors to operate in trains of 1920 Tube Stock. Some of these remained in service long after the rest of the 1906 Tube Stock was withdrawn, a couple remaining on the Aldwych branch until 1953.
1906 Stock at Golders Green station

[1] "Charing Cross Hamstead and Euston Railway", Railway Times (June 15 1907) p. 604
[2] "Charing Cross Hamstead and Euston Railway", Railway Times (June 22 1907) p. 628
[3] Mike Horne, The Bakerloo Line (Capital Transport, 2001) p. 13
[4] Mike Horne, The Northern Line (Capital Transport, 2009) p. 22 
[5] Desmond F. Croome, The Piccadilly Line (Capital Transport, 1998) p. 16 
[6] Piers Connor, The London Underground Electric Train (Crowood Press, 2015) p. 45
[7] Ibid. p. 83