The 1973 Tube Stock is a class of deep-level train that operates on the Piccadilly line of the London Underground. It was introduced into service in 1975 with the extension of the line to Hatton Cross Station in 1975, followed by a further extension to Heathrow Central Station in 1977. The entire fleet was refurbished by Bombardier Transportation between 1996 and 2001. From 2025, these trains will be replaced by New Tube for London trains, as part of the Piccadilly line modernisation programme, with all the '73 Stock trains scrapped by 2027/2028.
More information on the Wikipedia page [1]