No. 36 had double frames for the 4 ft 71⁄2 in (1.410 m) coupled wheels and an outside-frame bogie; cylinders were 20" x 24". The long boiler and raised round-topped firebox create a harmonious impression, and the loco acquired the nickname "The Crocodile". Among its innovative features included the use of Serve tubes.
Designed for heavy freights through the Severn Tunnel, it proved itself exceptionally capable. It was probably due to Dean's declining state of health and Churchward's increasing influence that the loco did little work away from Swindon, remained a prototype, and was withdrawn by Churchward in 1905 with the low mileage of 171,428.