The London Post Office Railway 1927 Stock was built by English Electric in 1927. Ninety of these four-wheeled units were built as the first stock used on the system.
Units were numbered 591–680, with trains formed of three units coupled together. However, these units were not very reliable and did not provide enough capacity for transporting mail through the capital. Therefore, they were soon replaced by fifty 1930 Stock units. These new units reused the electrical equipment from the 1927 Stock.
One unit, no. 601, has been preserved at Mount Pleasant workshops.
References
London Post Office Railway 1927 Stock Wikipedia(Text) CC BY-SA