This locomotive is a later Sentinel design, incorporating improvements over previous designs of this type. It includes a rear bunker of larger capacity, a larger water tank of fabricated construction, and the ability to change gear without leaving the loco cab, but the loco has to be stationary when so doing. Other minor improvements in cab controls were also made.

Built in 1952, No. 9537 was delivered new, with sister loco No. 9536, to the Chesterfield Tube Co., Derbyshire. Both locos were named after the children of a works director: No. 9536 became Timothy, and No. 9537, Susan.

In 1967 Timothy was part-exchanged for a Thomas Hill diesel loco, but his 'sister' Susan was sold for preservation to Mr. J. Morris of Lytham St. Annes, and exhibited in his "Motive Power Museum" from 1965. It was later sold to a QRS member, arriving at Quainton during 1984.

It was retubed, and restored to service in 1993. It is vacuum braked and has often hauled trains on Open Days. The locomotive is vertically boilered and has a chain drive between the crackshaft and axles.