Jack is a Dock Railway "rescue locomotive".
Jack was purchased in the 1970's as a kit by the Dock Railway from EMD. He was built from the wheels up as a EMD SD40-2 by Bigg City Rail Repairs. However, some careless workers built his rear-porch extra large, and placed a crane on it. The workers attempted to fix it, but it was too late, and he was painted and sent to the Dock Railway by flatbed truck.
He is friends with NREX 9402, and they work on the Dock Railway together.