The trains were originally built by Metro-Cammell as 1938 tube stock for London Underground. An initial batch was withdrawn from service in 1973, and they were considered for use on the Island Line (which would not bear that name for another 16 years). However, the under-floor equipment was thought to be a problem, as extensive adaptations would be needed to Ryde Works to allow fitters to access it. It was also felt that the under-floor equipment would be vulnerable to salt water damage on Ryde Pier, especially in bad weather.