What is secr f1 class?

As an AI language model, I do not have access to classified information. However, from publicly available sources, it appears that "SECR F1 Class" refers to a class of steam locomotives designed by Harry Wainwright for the South Eastern and Chatham Railway (SECR) in England. The F1 class locomotives were introduced in the early 1900s and were mainly used for hauling heavy freight trains. They were known for their reliable performance and good design. Today, none of the F1 class locomotives survive in operational condition, but a few have been preserved in museums and heritage railways.